Genetics

Question 1

Genotype

Answer 1

Genes responsible for a trait. A gene produces enzymes that catalyze a reaction to produce a trait.

Question 2

Phenotype

Answer 2

Expressed traits.

Question 3

Monohybrid

Answer 3

Only studying one trait.

Question 4

F1

Answer 4

First generation of offspring

Question 5

Allele

Answer 5

Version of a gene.

Question 6

Dominant gene

Answer 6

1. For Mendelian traits, a dominant allele is expressed over a recessive allele.
2. A recessive phenotype only has one genotype.

Question 7

Homozygous

Answer 7

The alleles agree on a trait (BB or bb)

Question 8

Heterozygous

Answer 8

Alleles don’t agree on a trait, so the dominant one is usually expressed (Bb).

Question 9

Codominance

Answer 9

Both traits are completely expressed, there is no dominant gene (blood type AB).

Question 10

Incomplete dominance

Answer 10

“In between” phenotype. The traits are combined. For example, a red flower and a white flower produce a pink flower.

Question 11

How are genotypes and phenotypes predicted?

Answer 11

A Punnett square predicts the probability of genetic combinations, usually 4 possibilities.

Question 12

Epistasis

Answer 12

The presence of a certain gene determines if another trait is expressed at all.

Question 13

Autosomes

Answer 13

Non sex chromosomes. Only one pair of chromosomes determines sex.

Question 14

What does each allele in a parent represent?

Answer 14

A gamete.

Question 15

3 laws of Mendelian Genetics

Answer 15

1. Law of Dominance
2. Law of Segregation
3. Law of Independent Assortment

Question 16

Law of Dominance

Answer 16

For a monohybrid cross, organisms with contrasting traits are studied. One parent is homozygous for dominant alleles, the other for recessive. All offspring are heterozygous for the F1 generation, but express the dominant trait. The traits don’t combine.

Question 17

Law of Segregation

Answer 17

1. When offspring reproduce among themselves, a recessive phenotype appears.
2. Alleles can segregate and recombine
3. If two heterozygous offspring reproduce, the phenotype is 3(B):1(b). The genotypes are 1(BB):2(Bb):1(bb).

Question 18

Law of Independent Assortment

Answer 18

1. If 2 traits are considered, 4 alleles are considered, and combine to make 4 gametes
2. Traits can segregate and combine independently, without being affected by other genes.

Question 19

Dihybrid Cross

Answer 19

1. Combines different alleles (8) for 2 traits to produce 16 possible combinations.
2. Best way to solve is to find the probability for each trait independently and then multiply them.

Question 20

Test Cross

Answer 20

1. Uses a recessive organism to determine the genotype of another organism if the genotype is unknown
2. If a recessive organism appears, the original organism was heterozygous

Question 21

Sex linked traits

Answer 21

A trait whose allele is carried on one of the sex chromosomes. Most are X linked.

Question 22

3 common X linked recessive traits

Answer 22

Hemophilia, color blindness, and male pattern blindness.

Question 23

How can a female express an X linked trait?

Answer 23

Can only express the trait if she is homozygous for the X chromosome that carries the allele (it appears on both X chromosomes).

Question 24

What is a carrier?

Answer 24

A person who carries the allele but does not express the trait. A female is a carrier if she is heterozygous for an X linked recessive trait. She can pass the allele to her offspring.

Question 25

How can a male express an X linked trait?

Answer 25

A male will express the trait if he carries it on his X chromosome. Although the trait is recessive, a male doesn’t have another X chromosome to cancel out the gene’s effects.

Question 26

Will the offspring of a male who expresses an X linked trait also express the trait if their mother is normal?

Answer 26

1. An X linked trait can’t pass from father to son because a father gives his son the Y chromosome. The male’s son will be normal.
2. A father gives his daughter another X chromosome. The daughter will be a carrier, but if her mother is normal she will not express the trait.

Question 27

Pedigree

Answer 27

1. A chart that shows the presence of a phenotype in a given family
2. Males are represented by squares, females by circles
3. Horizontal line represents mating, vertical shows offspring
4. Individuals with that phenotype are shaded.

Question 28

How to determine if a condition is dominant or recessive (pc)

Answer 28

Recessive conditions skip generations, so if neither parents nor offspring of an individual display the condition, it’s recessive.

Question 29

How to determine if a condition is sex linked or autosomal (pc)

Answer 29

Sex linked conditions are more common in males, so the condition is probably sex linked if many more males are affected than females.

Question 30

How to determine if an individual is homo or heterozygous for a condition (pc)

Answer 30

1. If an individual is female but not affected by a sex linked condition, she can’t be homozygous.
2. If a father has the condition but his daughter doesn’t, the daughter doesn’t, the daughter is heterozygous
3. All daughters of males affected by a sex linked condition are carriers.

Question 31

How to determine the possibility of producing an affected son/daughter (pc)

Answer 31

1. If the condition is autosomal, determine if it is dominant or recessive, then use a Punnett square with regular alleles. Sex doesn’t matter.
2. For a sex linked condition, make a Punnett square using chromosomes and the condition. Remember the probability of an affected father and a normal woman producing an affected son is 0%.