Incomplete Dominance / Sex - Linked Inheritance

Question 1

what is incomplete dominance

Answer 1

Both alleles are expressed but not completely as in co-dominance. Rather, the alleles are blended.

Question 2

see slide 46 - 47 for egs

Question 3

writing for incomplete dominance using flowers

Answer 3

The allelic symbols for incomplete dominance are always capitals

eg red flower R
white flower W

genotypes

red - RR

white - WW

pink - RW

Question 4

what do sex chromosomes determine

Answer 4

Two of them are called sex chromosomes and determine our gender.

Question 5

how do the sex chromosome relate to sex linked inheritance

Answer 5

They also have genes for other factors and the inheritance of them is called sex-linked inheritance.

Question 6

what is a consequence of sex linked inheritance

Answer 6

Because these genes are on the sex chromosomes, they can affect males and females differently.

Question 7

Do you know of any conditions that do not involve sex organs but which are more common in one sex than the other?

Answer 7

colour blindness

Question 8

why does the X chromosome contain more genes and what is the result of this?

Answer 8

The X chromosome is much
larger than the Y chromosome and therefore contains more genes (which are often inherited in a dom/recessive way

Question 9

writing used for sex linked inheritance using X and Y symbols

Answer 9

XR - dominant allele located on the X chromosome

Xr - recessive allele located on the X chromosome

(r/R in subscript)

Y- allele is on the Y chromosome but given that you usually only receive one Y chromosome, it is neither dominant or recessive.

Question 10

can both X and Y be dominant or recessive

Answer 10

no only X as you only recieve 1 Y chromosome

Question 11

hemizygous

Answer 11

Males only receive one copy of the gene on the X chromosome. This is called hemizygous

Question 12

Some conditions are X-linked recessive. How is it that these conditions affect males more commonly that females?

Answer 12

The conditions effect males because they don’t have the ability to inherit a second X chromsome with the dominant allele on it to overpower the ressesive allele, so if the males have the recessive allele, they have the trait.

Question 13

carrier

Answer 13

This means that the female is a heterozygote for a recessive condition.

XRXr - they “carry” the gene for the condition
(r/R in subscript)
but their phenotype does not show
the condition.

Question 14

do you use carrier as a phenotype?

Answer 14

Unless specifically asked for, DO NOT
give “carrier” as a phenotype outcome
from your punnett square.

eg you say Ff has freckles.
You don’t say that they are a “carrier”
of the non-freckle trait.

Question 14

see slide 46 - 47 for egs

Question 15

see slide 52 - 54 for egs

Question 16

why and how is a test cross done

Answer 16

A test cross is a test performed to determine whether an organism that displays a dominant phenotype is a
homozygote or a heterozygote.

The organism with the unknown genotype is ALWAYS crossed with a homozygote recessive.