Patterns of inheritance and variation

Question 1

Define gene

Answer 1

A sequence of DNA bases that code for an amino acid.

Question 2

Define alleles

Answer 2

Different versions of the same gene.

Question 3

Define genotype

Answer 3

An organism’s genetic makeup

Question 4

Define phenotype

Answer 4

An organism’s physical characteristics determined by its genotype and the environment

Question 5

Define dominant

Answer 5

An allele which is always expressed in the phenotype

Question 6

Define recessive

Answer 6

An allele which is only expressed when it is homozygous in the genotype

Question 7

Define locus (plural: loci)

Answer 7

The specific position of a gene on a chromosome

Question 8

Define homozygous

Answer 8

An organism with two identical alleles for a trait

Question 9

Define heterozygous

Answer 9

An organism with two different alleles for a trait

Question 10

Define codominant

Answer 10

Both alleles are equally dominant and expressed in the phenotype

Question 11

Define multiple alleles

Answer 11

More than two alleles for a single gene

Question 12

Define monohybrid/monogenic

Answer 12

Inheritance involves the transmission of one gene from parents to offspring

Question 13

Define dihybrid

Answer 13

Inheritance involves transmission of two genes from parents to offspring

Question 14

Define sex linkage

Answer 14

A gene whose locus is on the X chromosome

Question 15

Define autosomal linkage

Answer 15

Genes which are located on the same chromosome (but not the sex chromosomes)

Question 16

Define epistasis

Answer 16

When on gene modifies/masks the expression of a different gene at a different locus.

Question 17

What is the F1 generation in monohybrid crosses?

Answer 17

• Offspring from a cross between individuals with homozygous dominant and homozygous recessive alleles.
• All offspring are heterozygous.
• All offspring express dominant allele in their phenotype

Question 18

Describe the F2 generation in monohybrid crosses

Answer 18

• Offspring from a cross between two F1/heterozygous individuals.
• Results in offspring displaying 3:1 ratio of dominant to recessive phenotypes.

Question 19

How to show codominance in genetic diagrams.

Answer 19

• Uppercase letter is used to signify the gene
• Superscript uppercase letters indicate the alleles.

Question 20

Importance of multiple alleles

Answer 20

Increases the phenotypic diversity among individuals in a population

Question 21

Which gene controls the ABO blood group system?

Answer 21

Immunoglobulin/ I gene.

Question 22

If a genotype is IAIA or IAIO what is the phenotype and which antigens are present?

Answer 22

Blood type A
A

Question 23

If a genotype is IBIB or IBIO what is the phenotype and which antigens are present?

Answer 23

Blood type B
B

Question 24

If a genotype is IAIB what is the phenotype and which antigens are present?

Answer 24

Blood type AB
A and B antigens

Question 25

If a genotype is IOIO what is the phenotype and which antigens are present?

Answer 25

Blood type O None

Question 26

How to identify offspring phenotypes with multiple alleles.

Answer 26

- State the parents gametes (e.g. heterozygous for blood group A has gametes IA and IO) - Use a punnett square to identify potential phenotypes for offspring -State the phenotypic ratio

Question 27

Describe the inheritance of sex in humans.

Answer 27

Humans have 23 pairs of chromosomes, 22 of these are autosomes so are identical in males and females. The 23rd pair are sex chromosomes which differ between the sexes and determine an individuals sex.

Question 28

What two forms can the sex chromosome come in? Name and describe

Answer 28

X chromosome - found in both males and females. Y chromosome - found in males only. - Female body cells have two X chromosomes, XX so all egg cells contain an X chromosome. - Male body cells have an X and a Y chromosome, XY, so all sperm cells have an X or a Y chromosome.

Question 29

What are most sex linked genes? Why? What does this mean?

Answer 29

- X linked - X chromosome is larger in size - Recessive alleles tend to appear more in the phenotype of males as there is no corresponding allele on the Y chromosome to mask them.

Question 30

What is haemophilia?

Answer 30

An X-linked recessive disorder caused by a defective gene on the X chromosome. - alters DNA sequence for crucial blood clotting protein resulting in excessive bleeding.

Question 31

Facts about the inheritance of haemophilia

Answer 31

- Mostly affects males/ doesn't often affect females. - Always inherited from the mother in males - Mostly inherited from carrier mothers - Affected Fathers can only pass it on to daughters.

Question 32

How do linked genes (located on the same autosome) tend to be inherited in offspring?

Answer 32

Tend to be inherited together in offspring rather than assorting independently.

Question 33

Autosomal linkage means that...

Answer 33

- There is a non-random association of alleles at different loci - Parental allele combinations are preserved across generations - Phenotypic ratios observed in dihybrid crosses are different from those expected in independent assortment.

Question 34

The effects of crossing over on autosomal linkage

Answer 34

- Crossing over may separate linked genes - When genes ARE linked, fewer recombinant offspring tend to be produces, resulting in less genetic variation being introduced by crossing over. - The closer linked genes are on a chromosome, the more likely they are to be inherited together.

Question 35

What is the recombinant frequency?

Answer 35

A measure of how often recombinant offspring are produced as a result of crossing over.

Question 36

Recombination frequency formula

Answer 36

Recombination frequency = number of recombinant offspring/ total number of offspring

Question 37

What does a 50% recombination frequency indicate?

Answer 37

That there is no linkage between genes

Question 38

What does a recombination frequency below 50% indicate?

Answer 38

Signifies some degree of autosomal linkage

Question 39

What does a lower recombination frequency indicate?

Answer 39

The lower the recombination frequency, the closer the genes are on a chromosome meaning they are less likely to be separated in crossing over.