Inherited change

Question 1

What is a gene?

Answer 1

A length of DNA that codes for one polypeptide

Question 2

What is a locus?

Answer 2

The position of a gene on a chromosome

Question 3

What is an allele?

Answer 3

Alternative versions of a gene. (If more than 2, they are multiple alleles).

Question 4

What is the genotype?

Answer 4

The combination of alleles possessed by an organism

Question 5

What is the phenotype?

Answer 5

The observable characteristics of an organism due to a combination of genotype and the environment

Question 6

What is meant by homozygous?

Answer 6

When a genotype has the same 2 alleles of a gene, making the organism a homozygote

Question 7

What is meant by heterozygous?

Answer 7

When a genotype has different 2 alleles of a gene, making the organism a heterozygote

Question 8

What is meant by dominant?

Answer 8

An allele that is always expressed in the phenotype

Question 9

What is meant by recessive?

Answer 9

An allele that is only expressed in the phenotype of a homozygote

Question 10

What is meant by codominant?

Answer 10

Alleles which are both expressed in the phenotype (if they occur together)

Question 11

How are new genetic combinations created in meiosis?

Answer 11

Homologous chromosomes pair up and swap alleles during crossing over

Question 12

What type of cells does meiosis produce?

Answer 12

Gametes, which are genetically different

Question 13

What does a monohybrid cross involve?

Answer 13

The inheritance of one gene

Question 14

When is a characteristic sex-linked?

Answer 14

If the gene that codes for it is located on one of the sex chromosomes (X or Y)

Question 15

What sex chromosomes do females have?

Answer 15

XX

Question 16

What sex chromosomes do males have?

Answer 16

XY

Question 17

Why are males more susceptible to genetic disorders than females?

Answer 17

Because the Y chromosome is so small that it contains very few genes, so most sex-linked genes are located on the X chromosome. Due to males only having 1 X chromosome, if they carry a defective recessive allele, this WILL affect the phenotype as it is the only allele of the gene present.

Question 18

What happens if a female has a defective recessive allele of a gene on 1 X chromosome?

Answer 18

She will NOT suffer from the genetic disorder as long as her second X chromosome carries a normal dominant allele of that gene, She is called a carrier of the genetic disorder, due to being heterozygous.

Question 19

What type of alleles are most genetic disorders caused by?

Answer 19

Recessive alleles

Question 20

What would be evidence on a pedigree diagram that a disorder is recessive?

Answer 20

If 2 unaffected parents have an affected child (don’t forget to quote any numbers)

Question 21

What does a dihybrid cross involve?

Answer 21

The inheritance of 2 different genes

Question 22

What are the 3 types of dihybrid cross?

Answer 22

-Unlinked genes
-Epistasis
-Autosomal linked genes

Question 23

What do unlinked genes involve?

Answer 23

2 different genes on 2 different chromosomes that control 2 different characteristics

Question 24

What does epistasis involve?

Answer 24

2 different genes on 2 different chromosomes that control the same characteristic

Question 25

What do autosomal linked genes involve?

Answer 25

2 different genes on the same chromosome that control 2 different characteristics

Question 26

How is a Barr body formed?

Answer 26

Early in a female’s development, one X chromosome is unactivated, which then supercoils to form the Barr body.

Question 27

What is a Barr body?

Answer 27

A condensed, inactive X chromosome

Question 28

What are unlinked genes caused by?

Answer 28

The independent segregation which occurs in meiosis

Question 29

What is epistasis?

Answer 29

The interaction of different genes so that one gene controls the expression of alleles of another gene

Question 30

What are “linked” genes?

Answer 30

Genes for different characteristics that are located on the same chromosome

Question 31

What is autosomal linkage?

Answer 31

When 2 genes are located on the same autosome (non-sex chromosome), so are inherited together

Question 32

How does linkage with crossing-over alter the ratio of the genotypes and phenotypes of the offspring?

Answer 32

It results in more of 2 phenotypes than expected and less of the other 2 phenotypes