Module 6: Section 2 - Patterns of Inheritance Flashcards
What is continuous variation?
continuous variation is when the individuals in a population within a range - there are no distinct categories e.g. waist circumference / height
What is discontinuous variation?
discontinuous variation is when there are two or more distinct categories, there are no intermediates, e.g. blood group, or violet flower colour - they can be violet or white
How can variation be influenced by your genes?
1) different species have different genes
2) individuals of the same species have the same genes, but different versions of them (called alleles)
3) the genes and alleles an organism has make up its genotype
4) sexual reproduction leads to variation in genotypes within a species. Meiosis makes gametes with a unique assortment of alleles through crossing-over and the independent assortment of chromosomes. the random fusion of gametes during fertilisation also increases genetic variation in the offspring
5) the differences in genotype result in variation in phenotype - the characteristics displayed by an organism. variation in phenotype is also referred to as phenotypic variation
6) inherited characteristics that show continuous variation are usually influenced by many genes - these characteristics are said to be polygenic
7) inherited characteristics that show discontinuous variation are usually influenced by only one gene. Characteristics that are only controlled by one gene are said to be monogenic
Characteristics that are only controlled by one gene are…?
characteristics that are only controlled by one gene are said to be monogenic
Define polygenic characteristics
inherited characteristics that show continuous variation are usually influenced by many genes - these characteristics are said to be polygenic
define gene
a sequence of bases on a DNA molecule that codes for a protein, which results in a characteristic
define allele
a different version of a gene. most plants and animals, including humans, have two alleles of each gene, one from each parent. the order of bases in each allele is slightly different - they code for different version of the same characteristic. they’re represented using letters
define genotype
the alleles an organism has, e.g. BB, Bb or bb for eye colour
define phenotype
the characteristics the alleles produce, e.g. brown eyes
define dominant
my kink
HA no not really the answer is –> an allele whose characteristic appears in the phenotype even when there’s only one copy
define recessive
an allele whose characteristic only appears in the phenotype if two copies are present
define codominant
alleles that are both expressed in the phenotype - neither one is recessive, e.g. the alleles for Hb
define locus
the fixed position of a gene on a chromosome. alleles of a gene are found at the same locus on each chromosome in a pair
define homozygote
an organism that carries two copies of the same allele, e.g. BB
define heterozygote
an organism that carries two different alleles, e.g. Bb
define carrier
a person carrying an allele which is not expressed in the phenotype but that can be passed on to offspring
occasionally, alleles show codominance - what does this mean?
both alleles are expressed in the phenotype, neither one is recessive. e.g. the human allele for sickle cell anaemia
what is dihybrid inheritance and what does a dihybrid cross work out?
dihybrid inheritance is the inheritance of two characteristics which are controlled by different combinations of characteristics. you can use a dihybrid cross to look at how the two different genes are inherited at the same time
How are some characteristics sex linked?
1) the genetic info for gender is carried on two sex chromosomes
2) in mammals, females have two X chromosomes and males have one X and one Y chromosome
3) a characteristic is said to be sex-linked when the allele that codes for it is located on a sex chromosome
4) the y chromosome is smaller than the x chromosome and carries few genes. so, most genes on the sex chromosomes are only carried on the x chromosome (called x-linked genes)
5) as males only have one X chromosome, they often only have one allele for sex-linked genes. so, because they only have one copy, they express the characteristic of this allele even if it’s recessive. this makes males more likely than females to show recessive phenotypes for genes that are sex-linked
6) genetic disorders caused by faulty alleles on sex chromosomes include colour blindness and haemophilia. the faulty alleles for both of these disorders are carried on the X chromosome - they’re called X-linked disorders
What are X-linked disorders?
genetic disorders caused by faulty alleles on sex chromosomes include colour blindness and haemophilia. the faulty alleles for both of these disorders are carried on the X chromosome - they’re called X-linked disorders
Why are males more likely than females to express characteristics of recessive alleles that are sex-linked?
as males only have one X chromosome, they often only have one allele for sex-linked genes. so, because they only have one copy, they express the characteristic of this allele even if it’s recessive. this makes males more likely than females to show recessive phenotypes for genes that are sex-linked
How are some autosomal genes linked?
1) autosomal is a name for any chromosome that isn’t a sex chromosome
2) genes on the same autosome are said to be linked - because they’re on the same autosome they’ll stay together during the independent assortment of chromosomes in meiosis I, and their alleles will be passed on to the offspring together. The only reason this won’t happen is if crossing over splits them up first
3) the closer together two genes are on the autosome, the more closely they are said to be linked. This is because crossing over is less likely to split them up
4) if two genes are autosomally linked, you won’t get the phenotypic ratio you expect in the offspring of a cross
5) this allows you to use the predicted phenotypic ratio to identify autosomal linkage
