Chapter 17: Inherited Change

Question 1

A characteristic is sex-linked when

Answer 1

the allele that codes for the characteristic is found on one of the sex chromosomes (XX, XY)

Question 2

Why are most sex-linked genes only found on the X chromosome?

Answer 2

• the Y chromosome is smaller than the X chromosome
• can’t carry as much genetic info
• carries fewer genes

Question 3

Why are males more likely than females to show recessive phenotypes for genes that are sex-linked?

Answer 3

• most genes coding for sex-linked characteristics are found on the X chromosome because the Y chromosome is smaller/carries fewer genes
• males only have 1 X chromosome
• so they often have only one copy/allele of the gene for the sex-linked characteristic
• so the allele is expressed even if it is recessive

Question 4

Name a genetic disorder that is caused by faulty alleles found on sex chromosomes

Answer 4

colour blindness, haemophillia

Question 5

autosomal linkage

Answer 5

• when different genes are found on the same autosome
• inheriting one characteristic means inheriting the other
• inextricably linked *

Question 6

autosome

Answer 6

chromosomes that are not sex chromosomes

Question 7

Why are autosomal linked genes inherited together?

Answer 7

They stay together, on the same chromosome during independent segregation in meiosis I

Question 8

Why is it that the closer the genes are on the chromosome the more linked they are?

Answer 8

• crossing over is less likely to split them up

Question 9

What is the probability of a homozygous dominant allele (AA) in a population?

Answer 9

p²

Question 10

What is the probability of heterozygous alleles (Aa or aA) in a population?

Answer 10

2pq

Question 11

What is the probability of a homozygous recessive allele (aa) in a population?

Answer 11

q²

Question 12

What does p stand for?

Answer 12

p stands for the probability of the dominant allele in a population?

Question 13

What does q stand for?

Answer 13

q stands for the probability of a recessive allele being in a population?

Question 14

Why is this equation true?

p + q = 1.0

Answer 14

• because there are only two alleles

- we know that the probability of one plus the other is going to be 1.0 or 100%

Question 15

Why is this equation true?

p² + 2pq + q² = 1.0

Answer 15

there are only 4 possible arrangements of the two alleles, it follows that the probability of all four added together must equal 1.0

Question 16

What is the allelic frequency?

Answer 16

the number of times an allele appears within the gene pool of a population

Question 17

What is a gene pool?

Answer 17

• all the genetic info of all the individuals in a population
• all the alleles of all the genes of all individuals in a population at a given time
• the total number of alleles

Question 18

In monohybrid inheritance, the offspring of a pure-breeding dominant parent and a pure-breeding recessive parent are crossed to give the F2 generation. What is the theoretical ratio of this F2 generation and what is the genotype of the F1 generation?

Answer 18

The ratio is 3:1
3 offspring showing the dominant characteristic (AA,Aa)
1 offspring showing the recessive characteristic (aa)
the F1 generation are all heterozygous and show the dominant trait (Aa)
when they are crossed with each other it produces the 3:1 ratio

Question 19

What is monohybrid inheritance?

Answer 19

monohybrid inheritance is the inheritance of a single gene/characteristic

Question 20

What is it called when the heterozygous plants of an F1 generation are crossed with one another.

Answer 20

F1 intercross

Question 21

Why is it that the actual results of genetic crosses are rarely the same as the predicted results?

Answer 21

the fusion of gamete is random/determined by chance

Question 22

What is a ratio?

Answer 22

a ratio is a measure of the relative size of two or more cases that is expressed as a proportion

Question 23

What is the name given to the situation when a gene has more than 2 allelic forms? (human ABO blood group)

Answer 23

multiple alleles

Question 24

What is it called when two alleles both contribute to/are expressed in an organism’s phenotype?

Answer 24

codominance

Question 25

What is dihybrid inheritance?

Answer 25

dihybrid inheritance is the inheritance of 2 or more different genes that are located on different chromosomes

Question 26

Give an example of dihybrid inheritance.

Answer 26

seed shape and seed colour in pea plants
4 different arrangements of gametes:
GR, Gr, gR, gr
G = green
g = yellow
R = round seed
r = wrinkled seed