Chapter 9 Vocabulary

ABO blood groups

The ABO blood groups in humans involve three alleles of a single gene. Various combinations of these three alleles produce four phenotypes: A person's blood type may be A, B, AB, or O.

What of Mendel's laws:? 1. orientation of pairs of homologous chromosomes in Metaphase 1 2. Separation of pairs of homologous chromosomes in anaphase 1

1. Law of independent assortment 2. Law of segregation

1.Why is a testcross un- necessary to determine whether a snapdragon with red flowers is homo- zygous or heterozygous? 2. Maria has type O blood and her sister has type AB blood. What are the genotypes of the girls' parents?

1. Only plants homozy- gous for the dominant allele have red flowers; heterozygotes have pink flowers. 2. One parent is IAi, and the other parent is IBi.

1.What is meant by a sex- linked gene? 2. White eye color is a recessive sex-linked trait in fruit flies. If a white- eyed Drosophila female is mated with a red-eyed (wild-type) male, what do you predict for the numerous offspring?

1. a gene that is located on a sex chromosome, usually the X chromosome 2. All female offspring will be heterozygous (XRXr), with red eyes; all male offspring will be white-eyed (XrY).

Genes come in different versions called ________. What term describes the condition where the two copies are identical? What term describes the condition where the two copies are different? 2. If two plants have the same genotype, must they have the same phenotype? If two plants have the same pheno- type, must they have the same genotype? 3. You carry two alleles for every trait. Where did these alleles come from?

1. alleles; homozygous; heterozygous 2. Yes. No, one could be homozygous for the dominant al- lele, while the other is heterozygous. 3. One is from your father via his sperm and one is from your mother via her egg.

Using a standard 52-card deck, what is the probability of being dealt an ace? What about being dealt an ace or a king? What about being dealt an ace and then another ace?

1/13 - 4 aces - 52 cards 2/13 - 4/52 + 4/52 4/52 x 3/51 - since there are 3 aces left in a deck with 51 cards remaining

A man and a woman who are both carriers of cystic fibrosis have had three children without cystic fibrosis. If the couple has a fourth child, what is the probability that the child will have the disorder? 2. Peter is a 28-year-old man whose father died of Huntington's disease. Peter's mother shows no signs of the disease. What is the probability that Peter has inherited Huntington's disease?

1⁄4 (The genotypes and phenotypes of their other children are irrelevant.) 2. 1⁄2

Six possible genotypes for blood

A blood: Ia Ia or Ia i B Blood: Ib Ib or Ib i O blood: ii AB blood: Ia Ib

Pedigree

A family tree. In the pedigree, Square represents a male, and a Circle represents a female, colored symbols indicate that the person has the trait being investigated, and an unshaded symbol represents a person who does not have the trait. The earliest (oldest) generation is at the top of the pedigree, and the most recent generation is at the bottom. Notice that we cannot deduce the genotype of every member of the pedigree. When offspring has the trait and none of the parents do, then offspring is homozygous recessive.

sex-linked gene

A gene located on a sex chromosome

Character

A heritable feature that varies among individuals, such as flower color

testcross

A mating between an individual of a dominant phenotype but unknown genotype, and a homozygous recessive individual. The appearance of the offspring may reveal the original genotype. If genotype is BB then offspring all heterozygous. If genotype is Bb then expect 3:1 ratio/mix(not just one color/trait)

Inbreeding

A mating between close blood relatives. More likely to produce offspring homozygous for a harmful recessive trait.

Mendel hypothesis 4

A sperm or egg carries only one allele for each in- herited character because the two alleles for a char- acter segregate (separate) from each other during the production of gametes. This statement is called the law of segregation. When sperm and egg unite at fertilization, each contributes its alleles, restor- ing the paired condition in the offspring.

Law of segregation

A sperm or egg carries only one allele for each inherited character because the two alleles for a character segregate (Separate) from each other during the production of gametes

Genotype

An organisms genetic makeup (PP, Pp, or pp)

Phenotype

An organisms physical appearance such as purple or white flowers

Huntington's Disease - Dominant disorder

Dominant disorder:

achondroplasia:Dominant disorder

Dominant disorder: A form of dwarfism in which the head and torso develop normally but the arms and legs are short. Only heterozygotes have this disorder as homozygous dominant kills the embryo.

Gene locus

Each labeled band on the chromosome, a specific location of a gene along the chromosome

Trait

Each variant of a character, such as purple or white flowers

Sickle Cell Disease

Example of pleiotropy. Red Blood Cells produce abnormal hemoglobin proteins, making red blood cells a sickle shape.

Cross Fertilization

Fertilization of one plant by pollen from a different plant

Mendel Hypothesis 2

For each inherited character, an organism inherits two alleles, one from each parent. These alleles may be the same or different. An organism that has two identical alleles for a gene is said to be homozygous for that gene (and is called a homo- zygote). An organism that has two different alleles for a gene is said to be heterozygous for that gene (and is called a heterozygote).

The Chromosome theory of inheritance

Genes are located at specific positions (Loci) on chromosomes and that the behavior of chromosomes during Meiosis and fertilization accounts for inheritance patterns.

Sex Linked

Genes on the sex chromosomes (most often the X) are said to be sex- linked. Their inheritance pattern reflects the fact that females have two homologous X chromosomes, but males have only one X chromosome. Most sex-linked human disorders, such as red-green colorblindness and he- mophilia, are due to recessive alleles and are seen mostly in males. A male receiving a single sex-linked recessive allele from his mother will have the disorder; a female has to receive the allele from both parents to be affected.

carriers

Heterozygotes who are carriers of the recessive allele for the disorder but appear normal themselves

How does sickle-cell disease exemplify the concept of pleiotropy?

Homozygotes for the sickle-cell allele have abnormal hemoglobin, and its effect on the shape of red blood cells leads to a cascade of traits affecting many organs of the body.

F1 Generation

Hybrid offspring of the P generation

dihybrids

Hybrids heterozygous for both Characters in dihybrid cross

Mendel hypothesis 3

If the two alleles of an inherited pair differ, then one determines the organism's appearance and is called the dominant allele; the other has no noticeable ef- fect on the organism's appearance and is called the recessive allele. Geneticists use uppercase italic letters to represent dominant alleles and lowercase italic letters to represent recessive alleles.

If you mate a chocolate Lab with a black Lab of unknown genotype and you end up with a litter of three black puppies, do you know for certain the genotype of the black parent?

No. It could be BB and would always produce black puppies or Bb and just happened to have three black puppies in a row. Producing more puppies would increase confidence in the result.

Pleiotropy

One gene influences several characters

P generation

Parental Plants

Why was the development of purebred pea plant variet- ies critical to Mendel's work?

Purebred varieties allowed Mendel to predict the outcome of specific crosses and therefore to run controlled experiments.

Cystic Fibrosis (CF)

Recessive Disorder: Person with two copies of the recessive allele. Excessive secretion of very thick mucus from the lungs, pancreas, and other organs. Vulnerable to recurrent bacterial infections.

Punnet Square

Repeats the cross in a way that highlights the four possible combinations of gametes and the resulting four possible offspring in the F2 generation

polygenic inheritance

The additive effects of two or more genes on a single phenotypic character (opposite of pleitropy)

Dominant allele

The allele out of the two different alleles that determines the organisms's appearance.

Recessive allele

The allele out of the two different alleles that has no noticeable effect on the organisms appearance

incomplete dominance

The appearance of F1 hybrids falls between the phenotypes of the two parents. Heterozygotes

Genetic Cross

The cross fertilization itself to get a hybrid Cross-fertilization of two different varieties of an organism or two different species; hybridization

Law of independent assortment

The inheritance of one character has no effect on the inheritance of another. They are two different characters

dihybrid Cross

The mating of parental varieties differing in two characters

Hybrids

The offspring of two different purebred varieties

F2 Generation

The offspring of when F1 plants self fertilize or fertilize each other

monohybrid Cross

The parental plants differ in only one character - ex. flower color

Rule of multiplication

The probability of a dual event is the product of the separate probabilities of the independent events - for coins = 1/2 x 1/2 = 1/4. the Probability that an egg from a Bb dog will have the b allele is 1/2 and the probability that a sperm will have the b allele is also 1/2. By the rule of multiplication, the probability that two b alleles will come together at fertilization is 1/4.

Genetics

The study of Hereditry

Heredity

The transmission of traits from one generation to the next

Mendel Hypothesis One

There are alternative versions of genes that account for variations in inherited characters. For example, the gene for flower color in pea plants exists in one form for purple and another for white. The alternative versions of a gene are called alleles.

wild - type traits

Those seen most often in nature. Non necessarily specified by dominant alleles. By contrast, the phenotype of the corresponding recessive allele is seen only in a homozygote (aa). Recessive traits may in fact be more common in the population than dominant ones. For example, the absence of freckles is more common than their presence.

Purebred Varieties

Varieties for which self fertilization produced offspring all identical to the parent

codominant

both alleles are expressed in heterozygous individuals (IAIB) who have type AB blood. The expression of both alleles.

At the moment of fertilization in humans, what determines the sex of the offspring?

whether the egg is fertilized by a sperm bearing an X chromosome (producing a female offspring) or a Y chromosome (producing a male)