Section 7 - Chapter 17: Inherited Change - old

Question 1

Why do we resemble our parents but are not identical?

Answer 1

1. Inherit alleles/ genes from both parents. Fusion of gametes. Gametes are haploid.
2. When egg/sperm meet we have 2 copies of each gene
3. Some are dominant and recessive.

Question 2

What is a gene?

Answer 2

Short section of DNA on a chromosome, this is a sequence of nucleotide bases that code for a specific protein.

Question 3

What is an allele?

Answer 3

Different forms/versions of a gene

Question 4

What is the genotype?

Answer 4

The genetic constitution of an organism. Combination of alleles. e.g Bb. Can be influenced by environment/mutations

Question 5

What is the phenotype?

Answer 5

Observable or biochemical characteristics of an organism due to genotype/allele and the environment

Question 6

What does homozygous mean?

Answer 6

Where 2 alleles for a given gene are the same ( BB)

Question 7

What does heterozygous mean?

Answer 7

Where 2 alleles for a given gene are different (Bb)

Question 8

What does dominant allele mean

Answer 8

A dominant allele is always expressed in the phenotype

Question 9

What does recessive allele mean?

Answer 9

An allele that influences the phenotype if 2 copies are present

Question 10

What is codominance?

Answer 10

When 2 alleles have equal influence in the phenotype.

Phenotype can be a blend of both alleles (colour) or both features are represented separately (Blood Group)

Question 11

What did Mendel discover when he crossed tall and dwarf pea plants

Answer 11

• The gene that controls height in pea plants has 2 alternative forms called alleles
• The allele for tallness is dominant and allele for shortness is recessive.

Question 12

What are dihybrid crosses used

Answer 12

Shows how 2 characters determined by 2 different genes located on different chromosomes are inherited.

Question 13

What are multiple alleles

Answer 13

Where there are more than 2 alleles of which only 2 may be present at the loci of an individual’s homologous chromosomes

e.g blood group

Question 14

How many pairs of chromosomes do humans have

Answer 14

23 pairs

Question 15

What is the 23rd pair also known as and what are they for male and female

Answer 15

• 23rd pair is the sex determining chromosomes
• XX is female and XY is male

Question 16

Any gene that is carried on either X or Y chromosome is said to be …. and which is longer

Answer 16

• Sex-linked
• The X chromosome is longer and for most of the chromosome there is no equivalent homologous portion to match with the Y chromosome.

Question 17

What is haemophilia

Answer 17

• Defective gene on the x chromosome
• Blood clots slowly and internal bleeding
• Affected individuals have a mutated allele (recessive) which results in a non-functional protein

Question 18

Exam Question : Male fruit flies are more likely to show a phenotype produced by a recessive allele carried on the X chromosome. Explain why

Answer 18

As males have only 1 X chromosome they only need 1 recessive allele to show the phenotype however females must present 2 recessive alleles as they have 2 X chromosomes.

Question 19

Exam Question: During meiosis, when the X and Y chromosome pair up they dont form a typical bivalent. Explain why

Answer 19

X and Y chromosomes are different sizes so chromatids are unable to line up and form bivalent/ only short pairing region/ most of length not homologous.

Question 20

Couple 1 and 2 have the disorder and have 3 children in which 1 doesn’t have the disorder. How can you tell the disorder is caused by a dominant allele.

Answer 20

The couple have a son that doesnt have the disorder whilst they do.

They therefore must be heterozygous and as they have the disorder it must be dominant.

Question 21

Couple 3 and 4 dont have the disorder but their daughter does. How can you tell the condition is caused by a recessive allele.

Answer 21

3 and 4 dont have the disorder but their daughter does therefore they must be carriers and passed on their recessive alleles.

Question 22

In fruit flies, the genes for body colour and wing length are linked. Explain what this means

Answer 22

The genes are on the same chromosome

Question 23

What are the remaining 22 chromosomes (not sex determining) called and what is the name when genes are located on the same autosome.

Answer 23

• Autosomes. The name given to the situation where 2 or more genes are carried on the same autosome is called autosomal linkange

Question 24

Answer 24

Question 25

Why are the ratios of 2 phenotypes more than others in autosomal linkage

Answer 25

• Linked genes remain together during meiosis and therefore remain together when they pass into the gamete.
• Small numbers in other phenotypes are due to crossing over.

Question 26

Distinguish between sex-linkage and autosomal linkage

Answer 26

• In sex linkage the linked genes are on the same sex chromosome whereas in autosomal linkage they are on any chromosome other than the sex chromosomes.

Question 27

What is epistasis and give an example

Answer 27

• Epistasis arises when the allele of 1 gene affects or masks the expression of another in a phenotype. Coat colour in mice.

Question 28

What is a species

Answer 28

A group of similar organisms that can reproduce to produce fertile offspring

Question 28

What is a species

Answer 28

A group of similar organisms that can reproduce to produce fertile offspring

Question 29

What is a population

Answer 29

A group of organisms of the same species that occupies a particular area at the same time

Question 30

What is a Gene Pool

Answer 30

All the alleles of all the genes of all the individuals in a population

Question 31

What is Allele Frequency

Answer 31

Number of times a particular allele occurs within the gene pool (Usually given as a % or decimal)

Question 32

What is the Hardy Weinberg Principle

Answer 32

1. Predicts the frequencies of alleles in a population won’t change from generation to generation
2. Assumption that proportion of dominant and recessive alleles remain the same from generation. 5 conditions need to be met.

Question 33

What are the 5 conditions that mean Hardy Weinberg Principle can be used.

Answer 33

1. There is no selection - all alleles are equally likely to be passed on
2. No mutations take place
3. There is a large population
4. Mating within the population is random
5. No emigration/ immigration - no alleles enter or leave the population

Question 34

What can the 2 Hardy Weinberg equations be used for

Answer 34

1. Estimate the frequency of particular alleles
2. Test whether or not the HW principle applies to particular alleles - to test whether other factors affect allele frequencies.

Question 35

What is the equation for allele frequency

Answer 35

• p+q = 1, p= frequency of dominant allele. q = recessive allele.
• The total frequency of all the possible alleles for a characteristic in a population is 1.0.

Question 36

What is the equation for genotype frequency

Answer 36

• p² + 2pq + q² = 1 , p² = frequency of homozygous dominant. 2pq = heterozygous, q²= homozygous recessive.
• Total frequency of all possible genotypes. 3 genotypes.
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