Chapter 17 - Inherited Change

Question 1

What do the terms gene and allele mean?

Answer 1

Gene - a section of DNA that codes for a specific protein

Allele - a specific version of a gene

Question 2

What do the terms phenotype and genotype mean?

Answer 2

Phenotype - visible characteristics of an organism (determined by genotype and environment)

Genotype - genetic composition of an organisms (combination of alleles found)

Question 3

What do the terms dominant and recessive mean?

Answer 3

Dominant - alleles always visible in phenotype of an organisms if present on gene

Recessive - allele only visible in phenotype if in presence of another identical allele

Question 4

What do the terms homozygous and heterozygous mean?

Answer 4

Homozygous - alleles for a particular gene are identical (GG,gg)

Heterozygous - alleles for a particular gene are different (Gg)

Question 5

What does it mean to have multiple alleles? Provide an example

Answer 5

When a gene has more than 2 alleles

• e.g. Four blood groups - A, B, AB, O

Question 6

What does the term co-dominance mean? Provide an example

Answer 6

When both alleles contribute to/are expressed in phenotype

E.g. white cow coat and red cow coat = both shown creating roan coat

Question 7

What is monohybrid inheritance?

Answer 7

Looking at inheritance of a single gene + controlling a single characteristic

Question 8

What was the example for monohybrid inheritance?

Answer 8

Pea Pod Colour

GG or Gg = green pod

gg = yellow pod

Question 9

What are the rules applied to monohybrid inheritance for 2 homozygous parents

Answer 9

When two homozygous parents are combined

• In F1 GENERATION - all offspring will be heterozygous and show dominant phenotype
• in F2 GENERATION - will be a 3:1 ratio

Question 10

What are the chromosomal pairs for females and males?

Answer 10

Females = XX (homologous)

Males = XY (not homologous) - as Y is smaller

Question 11

What does it mean for something to be sex linked?

Answer 11

Any gene that is on the X or Y chromosome is said to be sex-linked

Question 12

What’s the key idea relating to sex linked diseases?

Answer 12

Going to be more common in males than females because they only need one allele to then show disease

• as only have one X chromosome which the gene is on
• females can be carriers but don’t show in phenotype

Question 13

When a male and female cross, what is the ratio produced?

Answer 13

1:1

50% male and 50% female

Question 14

What is haemophilia?

Answer 14

A genetic blood clotting disorder

Question 15

Where is the gene for haemophilia located?

Answer 15

Gene for factor VIII (protein involved in blood clotting) is located on X chromosome

Question 16

What are the dominant and recessive alleles for haemophilia?

Answer 16

X^H - functional factor VIII allele (healthy)

X^h - factor VIII doesn’t produce

Question 17

What are pedigree charts used for + list the symbols for:

Males
Females
Presence of characteristic or not

Answer 17

Used to trace inheritance of sex-linked characteristics

Males - represented by a square
Female - represented by a circle
Presence of characteristic - represented by shading in shape

Question 18

What is dihybrid inheritance? Give an example

Answer 18

Inheritance of two characteristics, determined by two different genes on different chromosomes at the same time

Seed colour - yellow or green
Seed shape - round or wrinkled
= yellow and wrinkled or yellow and round
= green and wrinkled or green and round

Question 19

What are the rules associated with dihybrid crosses?

1. Homozygous dominant with recessive homozygous
2. 2 heterozygous
3. Heterozygous with recessive homozygote

Answer 19

• if crossing a homozygous dominant parent with a recessive homozygous - all offspring will be heterozygous and have dominant phenotype
• if crossing 2 heterozygous offspring = 9:3:3:1 ratio
• if crossing a heterozygote with recessive homozygote = 1:1:1:1 ratio

Question 20

What is epistasis?

Answer 20

It occurs when 2 genes (usually on different chromosomes) interact together to affect the phenotype

• an allele of one gene may affect or mask expression of another gene

Question 21

What is chi-squared?

Answer 21

A statistical analysis test used to evaluate whether the difference between observed and expected data is statistically significant

• always begins with a null hypothesis + mainly used for categorical data

Question 22

What is the equation for chi-squared?

Answer 22

(observed-expected) ² / expected

Question 23

How is the degree of freedom worked out?

Answer 23

Number of categories - 1

Question 24

What does it mean in the following scenarios?

1. When chi-squared < critical value
2. When chi-squared > critical value

Answer 24

1. When chi-squared is less than critical value - you can accept the null hypothesis as there is no significant difference between observed and expected showing it is due to chance
2. When chi-squared is more than critical value - you can reject the null hypothesis as there is a significant difference between observed and expected showing it is not due to chance

Question 25

What is autosomal linkage?

Answer 25

Still dihybrid inheritance (two separate genes)

Can be:
- linked = two genes found on same chromosome
- unlinked = two genes occur on separate chromosomes

Question 26

In unlinked genes, how many potential gamete combinations are there?

AaBb

Answer 26

4 - AB, Ab, aB, ab

Question 27

When two heterozygous unlinked genes are crossed what ratio of offspring is produced?

AaBb x AaBb

Answer 27

9:3:3:1 ratio

• due to independent segregation

Question 28

In linked genes, how many potential gamete combinations are there?

AB on one autosome
ab on another autosome

Answer 28

2 - AB and ab

Question 29

What ratio is produced when the two gamete combinations are crossed in linked genes?

Answer 29

AB//ab x AB//ab
= 3:1 ratio (if no crossing over)

Question 30

What needs to be mentioned if:

a question asks you to explain the results of numbers of offspring that clearly show genes are linked…

Answer 30

• State which alleles are linked eg. usually dominant and recessive AB and ab
• State what gametes the parents will therefore mainly produce
• State that crossing over produces few of the other gametes (state what they are) eg. Ab and aB
• State that therefore that’s why you have a high number of offspring (eg. the phenotypes that there are many of) and very few offspring (eg. the phenotypes that there are very few of)