Bio-110 Chapter 9A & 9B
The physical traits of an organism are called its_____________.
Phenotype
A ____________is one particular variation of a character.
Trait
The most common phenotype in a natural population is referred to as the __________.
wild type The wild type refers to the typical phenotype of a particular trait for a species as it occurs in nature. This is in contrast to mutant forms that may result from selective breeding.
If you are a male, the Law of Independent Assortment indicates that your gametes contain _____.
A random mix of the chromosomes you inherited from each parent.
A gene that is located on a sex chromosome (X or Y chromosome) is __________.
A sex-linked gene Any gene found on a sex chromosome is a sex-linked gene.
In a certain plant, the alleles A, B, and C are dominant to the alleles a, b, and c. A plant with the genotype AABbcc will have the same phenotype as the plant with the genotype _____.
AaBBcc Individuals with one or two dominant alleles of a gene are indistinguishable, so AA and Aa have the same phenotype, as do Bb and BB.
Folk singer Woody Guthrie died of Huntington's disease, a degeneration of the nervous system that is caused by an autosomal dominant allele. Which statement below must be true?
At least one of Woody Guthrie's parents must have had Huntington's disease also. Except for the new mutations, which are quite rare, all individuals with dominant conditions have an affected parent. An affected individual, however, might not have affected offspring, just as coin tossing sometimes does not yield heads.
A ___________ is an inherited feature that varies from individual to individual.
Character
If an organism has two non-identical versions of a gene, the one that is expressed in the organism is called the ______________ allele.
Dominant
The_____________ is the genetic makeup of an organism.
Genotype
R = can roll tongue; r = can't roll tongue. A couple who both have the ability to roll their tongues have a son who is also a tongue-roller. The son is curious about whether he is homozygous or heterozygous for the tongue-rolling trait. How could he find out?
Have children with a woman who is a non-roller. If any of their children are non-rollers, then he is a heterozygote.
Imagine that a deaf male has a child with a hearing female. You know that the male must have the genotype dd, but the female could be either Dd or DD. If the couple's first child has hearing, can you determine the mother's genotype? (Hint: Draw Punnett squares for the two possible crosses.)
Her genotype cannot be determined. A hearing child with a deaf father (dd) must have the genotype Dd. This means that the mother must have contributed a D allele, which would be possible if she is either DD or Dd . The mother's genotype cannot be deduced from this child's genotype.
Use the Punnett square from the introduction and the ones you drew for Part A to select the three statements that are true about the inheritance of this form of deafness.
If a deaf child is born to hearing parents, both parents must be Dd. If a deaf man and a hearing woman have a deaf child, the mother's genotype must be Dd. The child of a deaf man and a DD hearing woman will definitely have hearing
A genetic cross involving parents that differ in a single character is called a __________________________.
Monohybrid Cross
How have Mendel's laws fared as we have learned more about cell biology and processes such as meiosis?
Our knowledge has helped to explain some of the exceptions to Mendel's laws of inheritance.
If an organism has two non-identical versions of a gene, the one that is not expressed in the organism is called the _____________ allele
Recessive
Seeds from a sexually reproducing plant are harvested and later planted under identical conditions. What characteristics should be expected of the resulting offspring?
The seedlings should differ from each other, depending on their genetic constitution. The independent assortment of chromosomes at meiosis introduces great genetic variability into sexual reproduction.
Why is it that men are responsible for the gender of their children?
Unlike women, who only contribute an X chromosome, men contribute either an X or a Y chromosome. This means that half of a man's offspring will get the X chromosome (female) and the other half will get the Y chromosome (male).
The sex chromosomes in humans that make an individual a male are __________. >
X and Y
Tay Sachs disease runs in Rebecca's family. When she looked at her family pedigree, she saw a shaded circle. This represented __________.
a female with Tay Sachs The circle indicates a female, and the shading indicates the disease.
Assume tall (T) is dominant to dwarf (t). If a homozygous dominant individual is crossed with a homozygous dwarf, the offspring will __________.
all be tall Like Mendel's original purple x white cross, all the F1 offspring will show the dominant phenotype. Draw a Punnett square for help.
If a homozygous dominant is crossed with a homozygous recessive for a given trait, the offspring will be __________.
all of the dominant phenotype The offspring of an AA x aa cross are all Aa and express the dominant phenotype.
If a homozygous dominant is crossed with a homozygous recessive for a given trait, the offspring will be __________.
all of the dominant phenotype The offspring of an AA x aa cross are all Aa and express the dominant phenotype.
Most human genes come in alternate versions called ___________.
alleles
Fetal cells may be removed along with fluid from the womb for genetic testing by a process known as __________.
amniocentesis In amniocentesis, a small amount of the amniotic fluid containing cells is extracted for testing.
An allele is __________.
an alternative version of a gene A diploid organism has two alleles for each autosomal gene. The two alleles are found at comparable locations on homologous chromosomes. The alleles may be identical or slightly different, but they affect the same genetic character.
The development of many different breeds of dogs from a single ancestor has been the result of _____.
artificial selection Human (artificial) selection is responsible for the evolution of domestic canines into the variety of breeds that exist today.
Close relatives who mate are more likely to have children with genetic diseases because __________.
close relatives are likely to carry the same genetic disorders So the likelihood of the right combination of alleles to create disease is greater.
The most common lethal genetic disease in the United States is _____.
cystic fibrosis One out of every 2,500 Caucasians of European descent develops this disease. (One out of 25 Caucasians is a carrier.) It is much rarer in other groups.
GgTt pea plants can produce __________ type(s) of gamete(s), and a ggtt plant can produce __________ type(s) of gamete(s).
four ... one GgTt individuals can produce the following gametes: GT, Gt, gT, gt. A ggtt plant can produce only gt.
The scientific study of the transmission of traits from one generation to the next is called __________.
genetics The study of genetics helps us understand inheritance.
Pea plants are tall if they have the genotype TT or Tt, and they are short if they have the genotype tt. A tall plant is mated with a short plant. Half the offspring are tall, and half are short. This allows us to conclude that the tall plant is __________.
heterozygous A testcross will reveal the genotype of the plant with the dominant phenotype; the presence of any offspring with the recessive phenotype indicates that the tall plant is heterozygous (Tt).
Mendel observed that pairs of alleles were separated or segregated in gametes and that they were rejoined in fertilization. We know that pairs of _____ are segregated in _____ and then are rejoined through fertilization.
homologous chromosomes ... meiosis
A plant with the genotype AABbcc is __________.
homozygous for two different genes An organism having a pair of identical alleles for a character is said to be homozygous for the gene controlling that character. In this case it is AA and cc.
In a testcross, the unknown individual (with an unknown genotype) is always crossed with a(n) __________.
homozygous recessive individual Because you know the genotype of the homozygous recessive individual, you can easily calculate the genotype of the unknown.
Cystic fibrosis can be inherited even if neither parent has the disease. This is because the disease __________.
is caused by a recessive allele The most common lethal genetic disease in the United States is cystic fibrosis, which is recessively inherited.
John and Jane are planning a family, but each has a brother who has sickle-cell disease, so they are concerned that their children may develop sickle-cell disease. Neither John, Jane, nor their respective parents have the disease. They consult a genetic counselor, who tells them that __________.
it's possible that none of their children will have the disease, but tests on both of them will be required to make sure The tests will determine if either or both carry the sickle-cell allele.
In humans, the __________ determines the sex of the offspring because __________.
male ... the male can contribute either an X or a Y chromosome In humans, the male parent determines the sex of the offspring because he produces both X- and Y-bearing sperm. Eggs can contribute only X chromosomes.
Color blindness is a recessive, sex-linked trait in humans that is located on the X chromosome. The color-blindness trait shows up only in males because __________.
males have only a single X chromosome and thus no wild-type allele to offset the recessive allele Therefore, the recessive allele will always be expressed in males whereas the female will only have color blindness if she receives the allele on both of her X chromosomes.
Mendel formulated his principles of inheritance based on _____.
observations on the outcomes of breeding experiments. The underlying processes were unknown at the time.
Several inherited disorders are much more common in close-knit religious communities, such as the Amish, than in the general population. This is at least partly due to the fact that __________.
people in such communities are more likely to marry relatives This increases the chances that two individuals will produce offspring homozygous for a harmful recessive trait.
The physical traits of an organism are called its _____.
phenotype The phenotype can be things such as flower color or seed shape.
Phenylketonuria (PKU) is an autosomal recessive disorder. Using P and p to represent the alleles, what is the genotype of a phenylketonuric person?
pp PKU is a recessive disorder, and all affected individuals must be pp.
Why are human males much more likely than human females to inherit the recessive condition hemophilia (a failure of the blood to clot properly)?
the gene for hemophilia is sex-linked A female has to have the hemophilia gene on both of her X chromosomes to be a hemophiliac. If a male has the gene for hemophilia on his X chromosome, he has hemophilia.
Cystic fibrosis, which is usually lethal before the age of reproduction, is a homozygous recessive trait. Cases continue to arise, however, even though people with the disease rarely reproduce. This is because __________.
the harmful allele is present along with a normal allele in heterozygous individuals who do not exhibit the disease, but one-fourth of the offspring of two heterozygote parents should be afflicted ' Cystic fibrosis is inherited as a Mendelian recessive, and affected individuals usually have unaffected parents, both of whom are carriers of the recessive allele.
As we now understand it, the Law of Independent Assortment applies _____.
to pairs of genes that are on different chromosomes, but NOT to pairs of genes that are close together on the same chromosome
