Biology A2 Chapter 17 - Inherited Change

Question 1

Define the term genotype

Answer 1

The genetic constitution of an organism, it describes all the alleles the organism has

Question 2

Define the term phenotype

Answer 2

The observable or biochemical characteristics of an organism - it is the result of the interaction between the expression of the genotype and the environment

Question 3

Define the term gene

Answer 3

A length of DNA, that is, a sequence of nucleotide bases, that normally code for a particular polypeptide

Question 4

Define the term allele

Answer 4

One of the different forms of a gene

Question 5

What does it mean if an organism is homozygous for a charcateristic?

Answer 5

If the alleles on each of the homologous chromosomes is the same, then the organism is homozygous for that characteristic

Question 6

What does it mean if an organism is heterozygous for a characteristic?

Answer 6

If the two alleles on homologous chromosomes are different then the organism is heterozygous for that characteristic

Question 7

What is a homozygous dominant organism?

Answer 7

An organism with two dominant alleles for a named characteristic

Question 8

What is a homozygous recessive organism?

Answer 8

An organism with two recessive alleles for a names characteristic

Question 9

Define the term codominant

Answer 9

When two dominant alleles are both expressed in the phenotype of an organism, meaning the phenotype is either a blend of the features, or both features are represented

Question 10

What does it mean if an organism has multiple alleles?

Answer 10

When a gene has more than two alleles, of which only two may be present at the loci of an individuals homologous chromosomes

Question 11

What is monohybrid inheritance?

Answer 11

The inheritance of a single gene

Question 12

What does the law of segregation state?

Answer 12

In diploid organisms, characteristics are determined by alleles that occur in pairs. Only one of each pair of alleles can be present in a single gamete

Question 13

What is dihybrid inheritance?

Answer 13

When two characteristics, determined by two different genes located on different chromosomes, are inherited together

Question 14

What is the expected ratio for dihybrid inheritance?

Answer 14

9:3:3:1

Question 15

What does Mendel’s Law of Independent Assortment state?

Answer 15

Each member of a pair of alleles may combine randomly with either of another pair

Question 16

Define the term sex linked

Answer 16

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

Question 17

Why are sex linked diseases such as haemophilia more common in males?

Answer 17

The X chromosome is longer than the Y chromosome so there may be no equivalent homologous portion of the Y chromosome for certain characteristics. Heamophilia is caused by a recessive allele only present on the X chromosome and hence males only need to inherit one recessive allele to have the disease, but females need to inherit two recessive alleles which is less likely

Question 18

What is an X-linked genetic disorder?

Answer 18

A disorder caused by a defective gene on the X chromosome

Question 19

Define the term autosomal linkage

Answer 19

When two or more genes are carried on the same autosome

Question 20

What is an autosome?

Answer 20

All the chromosomes that are not sex chromosomes

Question 21

What is epistasis?

Answer 21

When the allele of one gene affects or masks the expression of another in the phenotype

Question 22

In epistasis, what are the names of the genes:
1. Doing the suppressing
2. Being suppressed

Answer 22

1. Epistatic gene
2. Hypostatic gene

Question 23

When is the chi squared test used?

Answer 23

It is used to test the null hypothesis. It is a means of testing whether any deviation between the observed and the expected numbers is significant or not

Question 24

What criteria must be met for the chi squared test to be used?

Answer 24

• The sample size must be relatively large, that is, over 20
• The data must fall into discrete categories
• Only raw counts and not percentages can be used
• It is used to compare experimental results with theoretical ones