Inherited change Flashcards
What is a gene?
A length of DNA that codes for one polypeptide
What is a locus?
The position of a gene on a chromosome
What is an allele?
Alternative versions of a gene. (If more than 2, they are multiple alleles).
What is the genotype?
The combination of alleles possessed by an organism
What is the phenotype?
The observable characteristics of an organism due to a combination of genotype and the environment
What is meant by homozygous?
When a genotype has the same 2 alleles of a gene, making the organism a homozygote
What is meant by heterozygous?
When a genotype has different 2 alleles of a gene, making the organism a heterozygote
What is meant by dominant?
An allele that is always expressed in the phenotype
What is meant by recessive?
An allele that is only expressed in the phenotype of a homozygote
What is meant by codominant?
Alleles which are both expressed in the phenotype (if they occur together)
How are new genetic combinations created in meiosis?
Homologous chromosomes pair up and swap alleles during crossing over
What type of cells does meiosis produce?
Gametes, which are genetically different
What does a monohybrid cross involve?
The inheritance of one gene
When is a characteristic sex-linked?
If the gene that codes for it is located on one of the sex chromosomes (X or Y)
What sex chromosomes do females have?
XX
What sex chromosomes do males have?
XY
Why are males more susceptible to genetic disorders than females?
Because the Y chromosome is so small that it contains very few genes, so most sex-linked genes are located on the X chromosome. Due to males only having 1 X chromosome, if they carry a defective recessive allele, this WILL affect the phenotype as it is the only allele of the gene present.
What happens if a female has a defective recessive allele of a gene on 1 X chromosome?
She will NOT suffer from the genetic disorder as long as her second X chromosome carries a normal dominant allele of that gene, She is called a carrier of the genetic disorder, due to being heterozygous.
What type of alleles are most genetic disorders caused by?
Recessive alleles
What would be evidence on a pedigree diagram that a disorder is recessive?
If 2 unaffected parents have an affected child (don’t forget to quote any numbers)
What does a dihybrid cross involve?
The inheritance of 2 different genes
What are the 3 types of dihybrid cross?
-Unlinked genes
-Epistasis
-Autosomal linked genes
What do unlinked genes involve?
2 different genes on 2 different chromosomes that control 2 different characteristics
What does epistasis involve?
2 different genes on 2 different chromosomes that control the same characteristic
What do autosomal linked genes involve?
2 different genes on the same chromosome that control 2 different characteristics
How is a Barr body formed?
Early in a female’s development, one X chromosome is unactivated, which then supercoils to form the Barr body.
What is a Barr body?
A condensed, inactive X chromosome
What are unlinked genes caused by?
The independent segregation which occurs in meiosis
What is epistasis?
The interaction of different genes so that one gene controls the expression of alleles of another gene
What are “linked” genes?
Genes for different characteristics that are located on the same chromosome
What is autosomal linkage?
When 2 genes are located on the same autosome (non-sex chromosome), so are inherited together
How does linkage with crossing-over alter the ratio of the genotypes and phenotypes of the offspring?
It results in more of 2 phenotypes than expected and less of the other 2 phenotypes
