Chapter 9 Patterns of Inheritance (bio 1050) 11/5/20
CHECKPOINT: Which of Mendel's laws have their physical basis in the following phases of meiosis: (a) the orientation of homologous chromosome pairs in metaphase I; (b) the separation of homologous chromosomes in anaphase I?
(a) The law of independent assortment; (b) the law of segregation
incomplete dominance
A type of inheritance in which the phenotype of a heterozygote (Aa) is intermediate between the phenotypes of the two types of homozygotes (AA and aa).
Complete dominance
A type of inheritance in which the phenotypes of the heterozygote and dominant homozygote are indistinguishable.
Trait
A variant of a character found within a population, such as purple flowers in pea plants.
Sickle-cell disease explained:
An individual homozygous for the sickle-cell allele produces sickle-cell (abnormal) hemoglobin The abnormal hemoglobin crystallizes, causing red blood cells to become sickle-shaped The multiple effects of sickled-cells Damage to organs: Kidney failure, heart failure, spleen damage, and brain damage Other effects: Pain and fever, joint problems, physical weakness, anemia, and pneumonia
Carriers
An individual who is heterozygous for a recessively inherited disorder and who therefore does not show symptoms of that disorder but who may pass on the recessive allele to offspring.
F2 generation
The offspring of the F1 generation -F2 stands for second filial.
Hybrids
The offspring of two different varieties
F1 generation
The offspring of two parental (P generation) individuals -F1 stands for first filial.
9.15 The environment affects many characters: height is also influenced by __________, such as nutrition and exercise
environmental factors
Carrier screening, fetal testing, fetal imaging, and newborn screening can provide information for reproductive decisions but may create ...
ethical dilemmas.
amniocentesis
A technique for diagnosing genetic defects while a fetus is in the uterus. A sample of amniotic fluid, obtained by a needle inserted into the uterus, is analyzed for telltale chemicals and defective fetal cells.
chorionic villus sampling (CVS)
A technique for diagnosing genetic defects while the fetus is in an early development stage within the uterus. A small sample of the fetal portion of the placenta is removed and analyzed.
Both the __ and __ alleles are dominant to the i allele.
-IA abd IB -i
ultrasound imaging
A technique for examining a fetus in the uterus. High-frequency sound waves echoing off the fetus are used to produce an image of the fetus.
Mendel's Laws 9.1 The study of genetics has ancient roots: Hippcrates's idea that particles called "pangenes" travel from each part of an organism's body to the eggs or sperm and then are passed to the next generation is incorrect. Why?
-The reproductive cells are not composed of particles from somatic (body) cells-gametes are haploid and somatic cells are diploid -changes in somatic cells do not influence eggs and sperm.
Variations on Mendel's Laws 9.11 Incomplete dominance results in intermediate phenotypes: Mendel's laws are valid for all sexually reproducing species, but _____ often does not dictate ________ in the simple way Mendel's laws describe.
-genotype -phenotype
9.3 Mendel's law of segregation describes the inheritance of a single character: Mendel developed four hypotheses, described below using modern terminology: Whats the first hypothesis?
1) There are alternative versions of genes(called alleles) that account for variations in inherited characters. Alleles: alternative versions of a gene
CHECKPOINT: A plant of genotype AABbCC is crossed with an AaBbCc plant. What is the probability of an offspring having the genotype AABBCC? (Hint: Treat this as 3 separate monohybrid crosses.)
1/16 (that is, 1/2 * 1/4 * 1/2)
Mendel developed four hypotheses, described below using modern terminology: what's the second hypothesis?
2) For each character, an organism inherits two alleles of a gene, one from each parent. Homozygous: An organism that has two identical alleles for a gene Heterozygous: An organism that has two different alleles for a gene
The Chromosomal Basis of Inheritance 9.16 Chromosome behavior accounts for Mendel's laws: The chromosome theory of inheritance-
A basic principle in biology stating that genes are located on chromosomes and that the behavior of chromosomes during meiosis accounts for inheritance patterns. -holds that genes occupy specific loci (positions) on chromosomes, and it is the chromosomes that undergo segregation and independent assortment during meiosis.
9.5 The law of independent assortment is revealed by tracking two characters at once: Monohybrid cross-
A cross between two individuals that are heterozygous for one character (Pp × Pp in this case)
Pedigree-
A family genetic tree representing the occurrence of heritable traits in parents and offspring across a number of generations. A pedigree can be used to determine genotypes of matings that have already occurred. -can help determine individual genotypes.
9.12 Many genes have more than two alleles that may be codominant: multiple alleles-
A gene that has more than two alleles
Sickle Cell Disease (SCD)
A genetic condition caused by a mutation in the gene for hemoglobin. The mutation causes the protein to crystallize, which deforms red blood cells into a curved shape. Such blood cells produce a cascade of symptoms that can be life-threatening.
character
A heritable feature that varies among individuals
Huntington's disease
A human genetic disease caused by a dominant allele -a degenerative disorder of the nervous system that usually does not appear until a person is 35 to 45 years old. -Because the allele for Huntington's disease is dominant, any child born to a parent with the allele has a 50% chance of inheriting the allele and the disorder. This example makes it clear that a dominant allele is not necessarily "better" than a corresponding recessive allele.
genetic cross
A mating of two sexually reproducing individuals -cross-fertilization
Rule of addition:
A rule stating that the probability that an event can occur in two or more alternative ways is the sum of the separate probabilities of the different ways. -calculates the probability of an event that can occur in alternative ways.
Mendel developed four hypotheses, described below using modern terminology: what's the fourth hypothesis?
A sperm or egg carries only one allele for each inherited character because allele pairs separate (segregate) from each other during the production of gametes. -This statement is called the law of segregation-A general rule in inheritance that individuals have two alleles for each gene and that when gametes form by meiosis, the two alleles separate, each resulting gamete ending up with only one allele of each gene; also known as Mendel's first law of inheritance.
universal recipient blood type
AB
CHECKPOINT: An AaBbcc individual would be indistinguishable in phenotype from which of the following individuals: AAbbcc, aaBBcc, AabbCc, Aabbcc, or aaBbCc?
All except Aabbcc
CHECKPOINT: Predict the phenotypes of offspring obtained by mating a black Lab homozygous for both coat color and normal eyes with a chocolate Lab that is blind from PRA.
All offspring would be black with normal eyes (BBNN × bbnn → BbNn).
CHECKPOINT: Why doesn't the cross shown in Figure 9.11A support the blending hypothesis (see Module 9.1)?
Although two of the F2 offspring show a "blended" phenotype (pink flowers), the other two do not, and the white and red alleles are not lost to future generations.
The IA and IB alleles are codominant, meaning...
Both alleles are expressed in heterozygous individuals (IAIB), who have type AB blood.
CHECKPOINT: What is the primary benefit of genetic screening by chorionic villus sampling (CVS)? What is the primary risk?
CVS allows genetic screening to be performed very early in pregnancy and provides quick results, but it carries a risk of miscarriage.
CHECKPOINT: Why is the sickle-cell trait considered codominant at the molecular level?
Codominance means that both traits are expressed; a carrier for the sickle-cell allele produces both normal and abnormal hemoglobin.
CHECKPOINT: Imagine you have two different birds of the same species, a female with a yellow beak and a male with a blue beak. Design a simple experiment to test the blending hypothesis.
Cross the two birds and observe the resulting beak color in the offspring. The blending hypothesis predicts the appearance of all green beaks.
Linked genes
Genes located near each other on the same chromosome that tend to be inherited together.
What did Mendel hypothesize?
He hypothesized that there are alternative versions of genes (alleles), the units that determine heritable traits
CHECKPOINT: You use a testcross to determine the genotype of a Lab with normal eyes. Half of the offspring are normal and half develop PRA. What is the genotype of the normal parent?
Heterozygous (Nn)
Various combinations of three alleles—called ________—produce four phenotypes: A person's blood type may be A, B, AB, or O.
IA, IB, and i
CHECKPOINT: If Libby had a child, which phenotype would allow her to deduce her own genotype for certain?
If her child had a straight hairline (hh), then Libby would know that she herself must be Hh.
Mendel developed four hypotheses, described below using modern terminology: what's the third hypothesis?
If the two alleles of an inherited pair differ, then one determines the organism's appearance and is called the dominant allele and the other has no noticeable effect on the organism's appearance and is called the recessive allele Dominant allele: The allele that determines the phenotype of a gene when the individual is heterozygous for that gene. Recessive allele: An allele that has no noticeable effect on the phenotype of a gene when the individual is heterozygous for that gene.
what did Mendel experiment?
Mendel crossed pea plants and traced traits (variants of a character) from generation to generation
What did Mendel argue?
Mendel published one of the most influential papers in the history of biology. In it, he correctly argued that parents pass discrete "heritable factors" on to their offspring. -Mendel stressed that the heritable factors, today called genes, retain their individuality generation after generation. That is, genes are like playing cards: A deck may be shuffled, but the cards always retain their original identities, and no card is ever blended with another. Similarly, genes may be sorted, but each gene retains its identity.
Codominant
Inheritance pattern in which a heterozygote expresses the distinct trait of both alleles.
CHECKPOINT: In what way was Bateson and Punnett's success dependent upon failing at first?
The "failure" to obtain the expected results provided the insight that led to the discovery of linked genes.
universal donor blood type
O
CHECKPOINT: Describe three generations of your own family using the terminology of a genetic cross (P, F1, F2).
The P generation is your grandparents, the F1 your parents, and the F2 is you (and any siblings).
CHECKPOINT: How can two plants with different genotypes for a particular inherited character be identical in phenotype?
One could be homozygous for the dominant allele and the other heterozygous.
CHECKPOINT: An individual is heterozygous, Bb, for a gene. According to the law of segregation, each gamete formed by this individual will have either the B allele or the b allele. Which step in the process of meiosis is the physical basis for this segregation of alleles? (Hint: See Figure 8.13.)
The B and b alleles are located at the same gene locus on homologous chromosomes, which separate during meiosis I and are packaged in separate gametes during meiosis II.
CHECKPOINT: Peter is a 30-year-old man whose father died of Huntington's disease. Neither Peter's mother nor a much older sister shows any signs of Huntington's. What is the probability that Peter has inherited Huntington's disease?
Since his father had the disease, there is a 50% chance that Peter received the gene. (The genotype of his sister is irrelevant.)
CHECKPOINT: If most characters result from a combination of environment and heredity, why was Mendel able to ignore environmental influences in his pea plants?
The characters he chose for study were all entirely genetically determined and all his test subjects were raised in a similar environment.
Genetics
The scientific study of heredity
9.2 The science of genetics began in an abbey garden: Heredity-
The transmission of traits from one generation to the next
CHECKPOINT: Maria has type O blood, and her sister has type AB blood. The girls know that both of their maternal grandparents are type A. What are the genotypes of the girls' parents? Their mother is IAi; their father is IBi.
Their mother is IAi; their father is IBi.
What does sickle cell disease affect?
This disease affects the type of hemoglobin produced and the shape of red blood cells, and causes anemia and organ damage.
Dihybrid cross
a cross between two organisms that are each heterozygous for two characters being followed.
Punnett Square
a diagram used in the study of inheritance to show the results of random fertilization -shows the four possible combinations of alleles that could occur when these gametes combine
9.7 Mendel's laws reflect the rules of probability: The rule of multiplication:
a rule stating that the probability of a compound event is the product of the separate probabilities of the independent events -calculates the probability of two independent events both occurring.
The genetic disorders listed below, and in Table 9.9, are known to be inherited as dominant or recessive traits controlled by ....
a single gene.
Locus
a specific location of a gene along the chromosome
Recessive phenotypes result only from the homozygous genotype __
aa -NOT AA or Aa
9.18 Crossing over produces new combinations of alleles: During meiosis, crossing over between homologous chromosomes produces new combinations of ....
alleles in gametes
Unfortunately, both _________ and _____ pose some risk of complications, such as maternal bleeding, miscarriage, or premature birth.
amniocentesis and CVS
Low-density lipoprotein (LDL)
bad cholesterol
The favored explanation of inheritance then became the "blending" hypothesis, the idea that the hereditary materials contributed by the male and female parents mix in forming the offspring. The blending hypothesis was finally rejected. Why?
because it does not explain how traits that disappear in one generation can reappear in later ones.
9.0 Home tests can reveal information about your genetic heritage: As of 2018, over 12 million Americans have sought to learn about their genetic makeup. How?
by spitting into a tube and mailing it off for analysis
The letters of blood types (A, B, AB, or O) refer to what?
carbohydrates EX: carbohydrate A meaning type A blood
-Sickle-cell and nonsickle alleles are ....
codominant -the blood cells of heterozygotes contain both normal and abnormal (sickle-cell) hemoglobins
The most common lethal genetic disease in the United States is ...
cystic fibrosis
•Many traits are affected, in varying degrees, by both ....
genetic and environmental factors.
Within weeks of wanting to learn about their genetic makeup, Americans receive a report providing a dizzying array of ....
genetic information. -The surging popularity of these services proves how deeply many of us care about our genetic makeup.
genotype:
genetic makeup of an organism
Many characters result from a combination of _________.
heredity and environment. -For humans, exercise alters build; sun-tanning darkens the skin; experience improves performance on intelligence tests; and social and cultural forces greatly affect appearance.
Most people who have recessive disorders are born to normal parents who are both ...
heterozygotes
In most cases, only people who are ______ for the sickle-cell allele have sickle-cell disease.
homozygous
9.17 Genes on the same chromosome tend to be inherited together: Bateson and Punnett studied plants that did not show a 9:3:3:1 ratio in the F2 generation. What they found was an example of ...
linked genes
Carriers of sickle-cell disease have increased resistance to ....
malaria
Mendel's laws correlate with chromosome separation in ....
meiosis
9.8 VISUALIZING THE CONCEPT Genetic traits in humans can be tracked through family pedigrees: The inheritance of many human traits follows...
mendels laws
9.4 Homologous chromosomes bear the alleles for each character: Every diploid cell has what?
pairs of homologous chromosomes
9.13 A single gene may affect many phenotypic characters: Pleiotropy
occurs when one gene influences multiple characters.
ABO blood group
phenotype in humans that involves three alleles of a single gene. -genetically determined classes of human blood -The ABO blood group phenotypes, also called blood types, are A, B, AB, and O
The chromosomes in a homologous pair carry alleles of the same genes at the ...
same locations.
Human height is an example of ...
polygenic inheritance.
genetic screening
process of testing DNA to determine the chance a person has, or might pass on, a genetic disorder
Are most harmful alleles dominant or recessive?
recessive
9.10 New technologies can provide insight into one's genetic legacy: Because most children with recessive disorders are born to healthy parents, the genetic risk for many diseases is determined by whether the prospective parents are carriers of the .....
recessive allele.
•Linked genes can be separated by crossing over, forming ...
recombinant gametes.
Mendel chose true-breeding varieties. What are true-breeding varieties?
referring to organisms for which sexual reproduction produces offspring with inherited traits identical to those of the parents
9.9 Many inherited traits in humans are controlled by a single gene: Mutant trait:
refers to a trait that is less common in nature.
An example of pleiotropy in humans is ...
sickle-cell disease
9.14 A single character may be influenced by many genes: Polygenic inheritance
the additive effects of two or more genes on a single phenotypic character
Phenotype:
the expressed traits of an organism
law of independent assortment
the law that states that genes separate independently of one another in meiosis
9.6 Geneticists can use a testcross to determine unknown genotypes: Testcross-
the mating between an individual of unknown genotype for a particular character and an individual that is homozygous recessive for that same character
P generation
true-breeding parents -P as in parents
How did the field of genetics begin?
when an Augustinian monk named Gregor Mendel deduced the fundamental principles of genetics by breeding garden peas.
