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