Genetics 1 Flashcards
genetics
the study of heredity and variation in organisms
heredity
the passing on of characteristics from parent to offspring
variation
the differences that exist within a species or population
species
a group of organisms that can interbreed with each other and produce fertile offspring
what does genetics attempt to explain
the similarities and differences between parents and offspring
2 examples of variation in humans
eye colour, hair colour
2 examples of variation in plants (roses)
different shape and colour of petals
2 types of variation
inherited variations
acquired variations
inherited variations
differences due to different genes that are passed from generation to generation eg. eye colour, blood type
acquired variations
differences that arise during development and that are not passed on eg. accidental loss of limb
where is information contains
in definite structures called genes
where are genes located
on the chromosomes in the nucleus
3 features of a chromosome
thread-like structures
composed of DNA and protein
carries genes
number of chromosomes in the nuclei of an organism is usually
constant
diploid
2n
2 sets of chromosomes
haploid
n
1 set of chromosomes
in diploid cells, how are chromosomes found?
in matching pairs; homologous chromosomes
gene
unit of heredity \
composition of a gene
DNA
locus
position of a gene on a chromosome
alleles
alternative forms of a gene occupying the same locus on a pair of homologous chromosomes
what do alleles give rise to
variation in a species
alleles in a diploid cell
2 alleles for every characteristic
how many alleles are present in a gamete
1 (haploid)
genotype
genetic make-up of an organism
consists of many sets of alleles
phenotype
the visible expression of the genotype
depends on genotype and effect of environment
which plant did mendel use
garden pea
why did Mendel choose the garden pea (4 reasons)
- several pure breeding varieties available
- sharply contrasting and easily recognisable characteristics
- self-pollinating
- large numbers of offspring, easily
monohybrid inheritance
the study of inheritance of one characteristic
2 results from Mendel’s first cross
seeds collected from tall plants only produced tall plants and seeds collected from dwarf plants only produced dwarf plants
what did mendel reason
that the dwarf characteristic which reappeared in the F2 generation must have been present in the F1 plants, but as it did not show he called it recessive
Mendel’s first law
the law of segregation
the law of segregation
characters are controlled by a pair of factors that separate during gamete formation. Only one factor of each pair is present in a gamete
how to do a test cross
crossing the unknown genotype (TT) or (Tt) with the known homozygous recessive for this character (tt)
test cross: 2 results
if all of the offspring show the dominant character, then the dominant parent is homozygous
if any of the offspring show the recessive character, the dominant parent is heterozygous
incomplete dominance means
neither allele is expressed in the heterozygote
homozygous genotype
identical alleles for a characteristic
heterozygous genotype
different alleles for a characteristic
dominant
an allele that is always expressed
recessive
an allele that is only expressed when it is homozygous
