3.4 Inheritance Flashcards
What was Gregor Mendel experiment with pea plants? (3)
- first, crossed different varieties of purebred pea plants, then collected and grew the seeds to determine their characteristics
- next, he crossed the offspring with each other (self-fertilisation) and grow their seeds to similarity determine their characteristics
- these crosses were performed many times to establish reliable data trends (5000 crosses were performed)
What did Mendel discover from these experiments? (2)
- when he crossed 2 different purebred varieties together the results were not a blend (only one features would be expressed)
(Purebred tall and short pea plants crossed, all offspring developed into tall growing plants) - when Mendel self-fertilised the offspring, the resulting progeny expressed the 2 different traits in a ration of -3:1
(When tall growing progeny were crosses, tall and short pea plants were produced in a ration - 3:1)
What conclusions did Mendel draw from the results of his experiment? (5)
- organisms have discrete factors which determine features (genes)
- organisms possess 2 versions of each factor (alleles)
- each gamete contains 1 version of each factor (sex cells are haploid)
- parent contribute equally to the inheritance of offspring as a result of fission between randomly selected egg and sperm
- for each factor, one version is dominant over another and will be completely expressed if present
What are Mendels laws? (3)
- law segregation: when gametes form, alleles are separated os each gamete carries only 1 alleles for each gene
- Law of independent assortment: the segregation of alleles for one gene occur independent to that of any other gene
- Principle of dominance: recessive alleles will be masked by dominant alleles
What are caveats to Mendels? (2)
- law of independent assortment does not hold true for genes located on same chromosome
- not all genes show a complete dominance hierarchy - some genes show co-dominance or incomplete dominance
What are gametes?
Haploid sex cells formed by process of meiosis
Describe why haploid sex cells are haploid (3)
- during MI, homologous chromosomes are separated into different nuclei prior to cell division
- as homologous chromosomes carry the same gene, segregation of the chromosome also separate allele pairs
- as ganteries contain only 1 copy of each chromosome they carry only 1 allele for each gene
What does it mean if gametes are haploid?
The only possess 1 allele for each gene
- male and female gametes fuse during fertilisation the zygote will contain 2 alleles for each gene
How many alleles for each gene are located on a sex chromosome?
Males have only 1 allele for each gene on the sex chromosome as the chromosomes aren’t paired
How can combinations of alleles be categorised? (3)
- if the maternal and paternal alleles are the same, the offspring is homozygous for the gene
- if the maternal and paternal alleles are different, the offspring is heterozygous for the gene
- males only have 2 allele for each gene located on a sex chromosome and are hemizygous for that gene
What the gene composition for a specific trait called?
Genotype
(Either heterozygous or homozygous)
What is there observable characteristics of a specific trait called?
Phenotype
What is the phenotype determined by?
- genotype and environmental influences
What will the dominant allele do? (3)
- dominant allele will mask the recessive allele when in a heterozygous state
- homozygous dominant and heterozygous forms will be phenotypically indistinguishable
- the recessive allele will only be expressed in the phenotype when in a homozygous state
What is co-dominance?
Occurs when pairs of alleles are both expressed equally in the phenotype of a heterozygous individual
What kind of allele dominance do blood type A and B have?
Co-dominant
How do genetic diseases occur?
When mutations to a gene abrogate normal cellular function leading to the development of a disease phenotype
Only what kinds of alleles will result in an autosomal genetic diseases to occur?
Homozygous (both alleles are faulty)
What will occur to a heterozygous person with an recessive disease carrying allele?
They will not develop the disease
They will be carriers
What is an example of an autosomal recessive disease?
Cystic fibrosis
What is the type of allel which only requires one allele to cause a genetic disease?
Dominant alleles
What is an example of an autosomal dominant genetic disease?
Huntington’s disease
What occurs is a genetic disease is co-dominant alleles?
Only requires one copy of the faulty for the disease to occur
What kind of disease result will heterozygous individuals with co-dominant allele diseases have?
Milder symptoms due to the moderating influence of a normal allele
