8.1 Flashcards
why is genetic variation important
variation that arises as a result of genetic variation is key to survival and evolution of individuals
what is independent/random assortment
components of the chromosome pairs from father and mother are distributed into gametes randomly so any number of your 23 chromosomes could come from your maternal or paternal chromosomes introducing considerable genetic variation
when does crossing over occur
meiosis 1 - prophase 1
what is crossing over (recombination)
large multi-enzyme complexes cut and join parts of the maternal and paternal chromatids together at the chiasmata to exchange genetic material leading to genetic variation as new combinations of alleles arise
what is a gene/point mutation
miscopying of just one or a small number of nucleotides
what is substitution
one base is substituted for another
what is deletion
a base is completely lost in the sequence
what is insertion
an extra base is added to the sequence
what is chromosomal mutation
changes in the positions of genes within the chromosomes or entire chromosome is lost or duplicated during meiosis
define phenotype
the physical and chemical characteristics that make up the appearance of an organism
what is a gene locus
specific site of a gene
what is an allele
different versions of a gene
what does polygenic mean
phenotype traits are determined by several interacting genes
what is a test cross
individual is crossed with a homozygous recessive individual to reveal the parental phenotype
why the ratios predicted by genetic cross not be represented in the population
- combination of alleles in each gamete is completely random
- some offspring die before they can be sampled (seeds don’t germinate, embryos miscarry)
- inefficient sampling techniques
what is the law of segregation
Mendels law which states that one unit or allele for each trait is inherited from each parent to give two alleles for each trait, the segregation of alleles in each pair takes place when the gametes are formed and some alleles code for phenotypes that are dominant over others
what is the law of independent assortment
Mendels law that different traits are inherited independently of each other which means that inheritance of alleles for one phenotype has nothing to do with the inheritance of alleles of another characteristic
what does it mean if a gene has multiple alleles
there are more than two possible variants at a particular locus
what is codominance
both alleles are expressed and the proteins they code for act together without mixing to produce a given phenotype
what is a digenic (dihybrid) cross
representation of breeding experiments involving the inheritance of two pairs of contrasting characteristics at the same time
what are recombinant phenotypes
offspring that have different phenotypes to their parents as a result of recombination of the chromosomes during sexual reproduction
what is gene linkage
when genes for two characteristics are found on the same chromosome and are close together so they are linked and inherited as a single unit
what is homogametic
individual produces gametes that only contain one type of sex chromosome
what is heterogametic
individual produces gametes that contain two different types of sex chromosome
what is sex linkage
genes that are carried on the sex chromosome
what is a sex linked disease
a genetic disease that results from a mutated gene carried on the sex chromosome
what is haemophilia
a sex linked genetic disease in which one of the factors needed for clotting the blood is not made in the body
