chapter 16 - heredity and inheritance Flashcards
inheritance
transmission of traits from one generation to another
gene
small segment of DNA, containing a sequence of nucleotides that codes for a specific polypeptide
alleles
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)
genotype
combination of alleles for a particular gene
phenotype
expressed trait/outward experience, influenced by its genotype and the environment
homozygous
having two identical alleles of a particular gene (DD, dd)
heterozygous
having two different alleles of a particular gene (Dd)
dominant allele
expressed in both homozygous and heterozygous
recessive allele
expressed in only homozygous recessive genotype as recessive allele is masked by dominant allele
codominant trait
both alleles equally expressed in heterozygous
monohybrid inheritance
inheritance of a trait that is controlled by a single gene
why does observed ratio differ from expected ratio
observed ratio often differs from the expected ratio of 3:1 because of sample size (could be too small) and random nature of fertilisation
genetic diagram
- parental phenotype
- parental genotype
- gametes
- random fertilisation
- F1 genotype
- F1 phenotype
- F1 phenotypic ratio
codominance
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
multiple alleles
gene that exists in more than two different forms
ABO blood types
IA and IB > dominant over IO, IA and IB are codominant
explain how parents of blood group A and blood group B can have children of blood group O
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
chromosomes in male and female
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
mutation
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
albinism
- a recessive gene mutation
- no (melanin) pigments in the hair, skin and eyes
sickle cell anemia
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
down syndrome
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
mutagens
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))
variation
differences in traits between individuals of the same species
discontinuous vs continuous variation
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
variation
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)
why is genetic variation important
genetic variation is important to help organisms adapt and survive in changing environments due to selective advantage
natural selection
process where organisms with desirable genes and characteristics are “selected” or “favoured” to survive and pass on their genes to their offspring
evolution
gradual change in the inheritable characteristics of a population over time
mechanism of evolution
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
spontaneous mutation
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
homologous chromosomes
same length, same shape , same sequence of genes
