6.3 - Patterns of inheritance Flashcards
What is variation ?
- The term variation refers to the differences between living organisms.
How can variation be ?
- It can be between different species or within a single species.
What are the two types of variation ?
- Continuous
- Discontinuous
What factors cause variation ?
- Genetic
- Environmental
What is continuous variation ?
- Is when the individuals within a population vary within a range - there are no distinct categories e.g. humans can be in a range of height not just tall or short
- more examples, waist circumference fur length
What is Discontinuous variation ?
- This is when there are two or more distinct categories - each individual falls into one of these categories.
- ## E.g Blood group - A,B, AB or O
Explain how variation can be influenced by your genes
- Different species have different genes
- Individuals of the same species have the same genes but different alleles.
EXAMPLE: - Human blood group -there are three different blood
group alleles, which result in four different blood groups. - Inherited characteristics that show continuous variation are usually influenced by many genes
these characteristics are said to be polygenic. - Human skin colour is polygenic- it comes in loads of different shades of colour.
- Inherited characteristics that show discontinuous variation are usually influenced by only one gene
(or a small number of genes). Characteristics controlled by only one gene are said to be monogenic.
EXAMPLE:
Violet flower colour - can only be purple or white
What is variation in phenotype referred to as ?
Phenotypic variation.
How can sexual reproduction cause variation ?
- 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.
What is genotype ?
all of the alleles that an organism carries on its chromosomes
What is phenotype ?
the characteristics displayed by an organism.
How can the environment cause variation ?
- Variation can also be caused by differences in the environment, e.g. climate, food, lifestyle.
Characteristics controlled by environmental factors can change over an organism’s life.
What are examples of variation in the environment
What is intraspecific variation ?
- Organisms of the same species have different characteristics
What is monogenic inheritance ?
- Monogenic inheritance is the inheritance of one gene.
- ratio 3:1
What is a dominant allele ?
- A dominant allele is an allele that , when present is always expressed in the phenotype.
Define phenotype
- The phenotype is the expression of the genotype and its interaction with the environment
What is dihybrid inheritance ?
- Dihybrid inheritance is the inheritance of two genes.
What is the phenotypic ratio of offspring
- 9:9:3:1
