chapter 16 - heredity and inheritance

Question 1

inheritance

Answer 1

transmission of traits from one generation to another

Question 2

gene

Answer 2

small segment of DNA, containing a sequence of nucleotides that codes for a specific polypeptide

Question 3

alleles

Answer 3

different forms of the same gene. alleles occupy same relative position on a pair of homologous chromosomes (exist in pairs, one chromosome in the pair is from the male parent, one chromosome is from the female parent, same sequence of gene loci)

Question 4

genotype

Answer 4

combination of alleles for a particular gene

Question 5

phenotype

Answer 5

expressed trait/outward experience, influenced by its genotype and the environment

Question 6

homozygous

Answer 6

having two identical alleles of a particular gene (DD, dd)

Question 7

heterozygous

Answer 7

having two different alleles of a particular gene (Dd)

Question 8

dominant allele

Answer 8

expressed in both homozygous and heterozygous

Question 9

recessive allele

Answer 9

expressed in only homozygous recessive genotype as recessive allele is masked by dominant allele

Question 10

codominant trait

Answer 10

both alleles equally expressed in heterozygous

Question 11

monohybrid inheritance

Answer 11

inheritance of a trait that is controlled by a single gene

Question 12

why does observed ratio differ from expected ratio

Answer 12

observed ratio often differs from the expected ratio of 3:1 because of sample size (could be too small) and random nature of fertilisation

Question 13

genetic diagram

Answer 13

1. parental phenotype
2. parental genotype
3. gametes
4. random fertilisation
5. F1 genotype
6. F1 phenotype
7. F1 phenotypic ratio

Question 14

codominance

Answer 14

codominance : both alleles (codominant) of a gene controlling a trait express themselves in the heterozygote, which has a phenotype intermediate between that of its pure-bred parents

Question 15

multiple alleles

Answer 15

gene that exists in more than two different forms

Question 16

ABO blood types

Answer 16

IA and IB > dominant over IO, IA and IB are codominant

Question 17

explain how parents of blood group A and blood group B can have children of blood group O

Answer 17

IA and IB alleles are dominant to IO allele / IO allele is recessive to Ia and Ib alleles
blood group O children are homozygous recessive with IOIO can inherit one Io allele form each parent/each parent pass down/ contribute one Io allele who are IAIO

Question 18

chromosomes in male and female

Answer 18

male
- body cell : 22 pairs of autosomes + XY
- gamete : 22 autosomes + X / 22 autosomes + Y

female
- body cell : 22 pairs of autosomes + XX
- gamete : 22 autosomes + X

Question 19

mutation

Answer 19

change in the structure/sequence of a gene or in the chromosome number

spontaneous and occurs on its own

two types : gene and chromosome mutation

Question 20

albinism

Answer 20

• a recessive gene mutation
• no (melanin) pigments in the hair, skin and eyes

Question 21

sickle cell anemia

Answer 21

a gene mutation which causes a change in the sequence of bases, changing the sequence of amino acids, changing the polypeptide formed, HbS protein is synthesised instead instead fo HbA, causing the red blood cells to be sickle shaped

Question 22

down syndrome

Answer 22

each chromosome has two copies, but people with down syndrome have three copies of chromosome 21, causing the person to have 47 chromosomes instead of the usual 46

Question 23

mutagens

Answer 23

agents in the environment that increase the rate of mutation in an organism (eg. ionising radiation (x-ray, gamma rays, beta rays) and certain chemicals (mustard gas, formaldehyde))

Question 24

variation

Answer 24

differences in traits between individuals of the same species

Question 25

discontinuous vs continuous variation

Answer 25

discontinuous :
- involves a few clear cut/distinct phenotypes
- controlled by one or a few genes
genes do not show additive effect
- relatively unaffected by environmental conditions
- examples : blood groups, gender, eye colour

continuous :
- involves a range of phenotypes
- controlled by many genes
- genes show additive effect
- greatly affected by environmental conditions
- examples : height, weight, skin colour

Question 26

variation

Answer 26

caused by :
- crossing over and independent assortment of chromosomes during meiosis
- mutation in genetic material that provides new alleles to the gene pool for natural selection to act on
- random fertilization of sperm and ovum (fusion of different gametes)

Question 27

why is genetic variation important

Answer 27

genetic variation is important to help organisms adapt and survive in changing environments due to selective advantage

Question 28

natural selection

Answer 28

process where organisms with desirable genes and characteristics are “selected” or “favoured” to survive and pass on their genes to their offspring

Question 29

evolution

Answer 29

gradual change in the inheritable characteristics of a population over time

Question 30

mechanism of evolution

Answer 30

organisms reproduce rapidly as food supply in abundant → organisms migrate to different environments → spontaneous mutation occurs, resulting in variation in the organisms. favourable traits will confer a selective advantage and such organisms will survive, reproduce and pass on their favourable traits to their offspring → organisms become the predominant species in environment, resulting in evolution of the species

Question 31

spontaneous mutation

Answer 31

spontaneous mutation results in genetic variation in the population. the environment act as the selection pressure and the trees that are resistant to the environment will survive and reproduce as a result of natural selection. they pass on the favourable genes of being resistant to their offspring and they evolve to resist the environmental change

Question 32

homologous chromosomes

Answer 32

same length, same shape , same sequence of genes