V4 Inheritance 6

• Biologie
• Middelbare school
• vwo
• Leerjaar 4

Welcome!

Have the following ready:

• Have joined the lessonup
• Have the dihybrid cross worksheet open on your computer

Roadmap for today:

First half, with the whole group:

• discuss dihybrid cross worksheet
• introduction to non-Mendelian inheritance (take notes!)

*break*

Second half, individually or in small groups:

• practice with sex-linked inheritance (worksheet)
• practice with codominance 

What is/are correct ways to write the genotype for heterozygous brown-eyed, curly-haired?

1. AaBb
2. BbcC
3. BrCs
4. BbCc

What are the possible gametes for someone with the genotype AaBB?

1. Aa, BB, AB, and aB
2. AB and aB
3. AaBB, AABB, and aaBB

Dihybrid cross worksheet Q1: What is the chance of producing offspring with phenotype Tall/Green?

1. 25%
2. 50%
3. 75%
4. 100%

Dihybrid cross worksheet Q2: What is the phenotypic ratio of the offspring?

Dihybrid cross worksheet Q3: What are the genotypes of the parent dogs?

1. DdRr and DdRr
2. DDRr and DdRR
3. DDRR and DDRR
4. DDRr and DdRr

Dihybrid cross worksheet Q3: How do you know that the genotypes of the parent dogs are both DdRr?

Dihybrid cross worksheet Q3: What is the phenotypic ratio of the offspring?

1. 3:1:0:0
2. 9:3:3:1
3. 1:1:1:1
4. 9:2:2:2

Non-mendelian inheritance

Mendel’s model of inheritance assumes that:

• Each trait is controlled by a single gene
• Each gene has only 2 alleles
• There is a clear dominant-recessive relationship between the alleles

Most genes do not meet these criteria.

Can you think of an example of non-Mendelian inheritance?

Polygenic inheritance

Polygenic inheritance occurs when multiple genes are involved in controlling the phenotype of a trait. The phenotype is an accumulation of contributions by multiple genes. These traits show continuous variation and are referred to as quantitative traits. 

For example: human height

Continuous variation

When multiple genes act together to produce a physical (phenotypic) character, a gradation or range of differences occur.

Pleiotropy

Pleiotropy refers to an allele that has more than one effect on the phenotype. 

Examples: diseases such as sickle cell anemia and cystic fibrosis. In these diseases, multiple symptoms can be traced back to one defective allele.

Incomplete dominance

Situation where 2 alleles 'blend' to form a hybrid ("inbetween") phenotype.

Co-dominance

In codominance, both traits appear. 

Co = together

Sex-linked inheritance

Gene is located on the X or Y chromosome.

In practice almost always on the X.

Inheritance: what have we done so far and what is still to come?

Done:

• Vocabulary: genes, alleles, homozygous, heterozygous, dominant, recessive, carrier...
• Incomplete dominance
• Monohybrid crosses
• Dihybrid crosses

Started:

• Sex-linked inheritance
• Co-dominance

Still to come

• Multiple alleles
• Lethal alleles
• (Epigenetics)

Self-directed work time:

Mandatory:

• Worksheet sex-linked inheritance
• Exercises Codominance

Optional: 

• Check answers dihybrid cross worksheet
• extra exercises dihybrid cross
• choose an article about genetics to read (see Classroom or ScienceNews.org)
• help your classmates
• study

You may work together (put everyone's names in the worksheet title)