Genetics Flashcards
Genotype
the alleles of an organism
Phenotype
the characteristics of an organism
Dominant allele
an allele that has the same effect on the phenotype whether it is present in the homozygous or heterozygous state
Recessive allele
an allele that only has an effect on the phenotype when present in homozygous state
Codominant alleles
pairs of alleles that both affect the phenotype when present in a heterozygote
Locus
the particular position on homologous chromosomes of a gene
Homozygous
having two identical alleles of a gene
Heterozygous
having two different alleles of a gene
Carrier
an individual that has one copy of a recessive allele that causes a genetic disease in individuals that are homozygous for this allele
Test cross
testing a suspected heterozygote by crossing it with a known homozygous recessive
State that some genes have more than two alleles (multiple alleles).
Some genes have more than two alleles (multiple alleles).
Describe ABO blood groups as an example of codominance and multiple alleles.
- three alleles controlling ABO blood groups
- if more than two alleles -> multiple allele
- IA (dominant) – Blood group A
- IB (dominant) – Blood group B
- IA + IB = AB (IAIB)
- ii -> homozygous for I – blood group O
- i = recessive allele
- both allele affect phenotype (dominant)
- Codominant allele = pairs of allele affecting phenotype when present in heterozygote
Explain how the sex chromosomes control gender by referring to the inheritance of X and Y chromosomes in humans.
- females: XX
- males: XY
- X chromosome is large, containing many genes
- Y chromosome smaller, containing fewer genes
- female always passes on X gene to offspring
- gender of offspring depends on sperm carrying X or Y
State that some genes are present on the X chromosome and absent from the Y chromosomes in humans.
Some genes are present on the X chromosome and absent from the Y chromosomes in humans.
Define sex linkage.
Sex linkage – when the gene controlling the characteristic is located on the sex chromosome and so we associate the characteristic with gender.
State that human female can be homozygous or heterozygous with respect to sex-linked genes.
Human female can be homozygous or heterozygous with respect to sex-linked genes.
Explain that female carriers are heterozygous for X-linked recessive alleles.
- females require dominant + recessive allele to be carrier
- inherit recessive from one parent and dominant from other parent
- example: haemophilia
Deduce the genotypes and phenotypes of individuals in pedigree charts.
- squares – males
- circles – females
- shaded – affected individuals
- unshaded – unaffected individuals
- if most males affected -> disease is X linked
- if 50/50 -> autosomal
- if dominant -> one parent must have disorder
- if recessive -> neither parent has to have disorder when heterozygous
1st stage of meiosis I
Prophase I
- chromosomes coil up tightly, become visible
- homologous chromosomes pair up
- crossing over occurs
- nuclear membrane disintegrates, centrioles travel to poles
2nd stage of meiosis I
Metaphase I
- microtubules form spindle
- spindle fibres attach to centromeres of chromosomes
- pairs of homologous chromosomes align on equator
3rd stage of meiosis I
Anaphase I
- spindle fibres shorten, pulling homologous chromosomes in opposite directions
- paired homologous chromosomes paired
- pulled to opposite poles
4th stage of meiosis I
Telophase I
- nuclear membrane forms around chromosomes at each pole
- chromosomes uncoil
- cell undergoes cytokinesis, forming two daughter cells
- forms two haploid cells
- at end cells either enter short interphase period or proceed to meiosis II
- DNA is not replicated
1st stage of meiosis II
Meiosis II Prophase II - chromosomes coil up again - centrioles move to cell poles - nuclear membrane disintegrates
2nd stage of meiosis II
Metaphase II
- spindle fibres attach to centromeres
- chromosomes align to equator
