Pack 18 - Genetics and Inheritance Flashcards
Define Genotype
combination of all alleles of an organism
Define Phenotype
expression of the genotypes and interaction with the environment
What does homozygous mean?
pair of chromosomes made of identical alleles
What does heterozygous mean?
pair of chromosomes made of different alleles
What is the monohybrid cross?
two gametes fuse (with both containing an allele for somthing i.e height)
the gene for height has two allelic forms which are dominant and recessive (e.g tall and short)
dominant allele always displayed if present
recessive allele only displayed if there are two recessive alleles
always a 3:1 ratio
What is backcross?
a way of determining the genotype of an unknown organism
cross unknown with recessive phenotype as these always have a homozygous genotype
if any resulting offspring are the homozygous recessive phenotype, the unknown genotype must be heterozygous
if all offspring have the dominant phenotype, the unknown genotype must be homozygous dominant
What is Codominance?
when a gene has two alleles and neither can dominate the alleles are said to be codominant
both alleles expressed in the phenotype
always a 1:2:1 ratio
what is multiple alleles?
some genes have more than two allelic forms
each individual can only have two alleles for each gene but the combinations are more varied
patterns of dominance need to be studied
what is sex determination?
sex is determined by the combination of chromosomes in a zygote, rather then the genes themselves
sex chromosomes are of 1 of 2 types (large X chromosome/small Y chromosome)
there us always a 50% probability of 2 parents producing a male/female child
what is sex linkage?
genes carried on sex chromosomes are unrelated to sexual characteristics but are inherited in different ways in males and females
these are said to be sex-linked genes and characteristics
What do you take into account when answering a sex linkage questions?
identifying both the sex and the phenotype for the condition
What is dihybrid inheritance?
how 2 different genes, coding for two different characteristics, are inherited
9:3:3:1 is always the ratio
What is epistasis?
when the allele of one gene affects or masks the expression of another in the phenotype
what is autosomal linkage?
all non sex chromosomes are autosomes
genes on the same chromosome are said to be linked
ratio is always 8:1:1:8
what is crossing over?
exchange of alleles between chromatids of homologous chromosomes during the first division of meiosis
