Recapping CHROMOSOMES

What is a Eukaryotic Chromosome?

• Chromosomes are lengths of _____ wound around protein (histone).

• Each chromosome contains many genes in a set order.

• Chromosomes are found in identical pairs (homologous pairs) in the ______ of each cell.

• One of each pair came from ____ and one from ____.

Homeobox genes - Starter• Homeobox genes control the development of the

_____ _____ of an organism, including the ______ and positioning of the ______.

• In Drosophila, which genes determine polarity?• determine segment polarity?• determine segment identification and

development?• How many base pairs in a homeobox?• How do some homeobox genes called transcription

factors work?• Drosophila has 2 Hox Clusters of homeobox genes,

activated from head to tail of the embryo. How many do i) Nematodes and ii) Vertebrates have?

• Retinoic acid is a morphogen – what does that do?• Vit A is stored in mammalian livers. Suggest why

pregnant women are advised not to eat liver.

AIMS• Go through Test on Tuesday• Collect exam question booklets• Chromosomes• Meiosis – work through in pairs with

plasticine and beads whilst I see everyone else about resits.

• Homework – Complete pages 9 – 14 in Meiosis booklet.

Task - Pair and Share

• Draw a chromosome before and after DNA Replication.

• Label where appropriate:-• Genes / centromere / chromatid.• Each gene codes for the expression

of a set characteristic.• Alleles are different forms of each

gene, e.g. for tongue rolling or not tongue rolling.

Chromosome number is fixed.

• e.g. Horse 64• Rice 12• Mouse 40• Sunflower 34• Human ?

• What do you notice about these numbers?• What would their haploid numbers be?

Here are all 46 of our chromosomes.

Diploid / Haploid

• Most animals and many plants have diploid somatic cells and haploid gametes.

• Haploid can be represented as n.• Diploid is then represented as __.• If n = 35 in a camel, how many

chromosomes are there in i) a somatic cell and ii) a gamete?

Homologous pairs

• Draw an annotated homologous pair of chromosomes.

• Key points / labels• Structure / centromere / gene

sequence / gene locus (loci) / alleles / homozygous / heterozygous

• Define locus, allele, homozygous, heterozygous (if not already done) and genome.

AIMS - http://www.youtube.com/watch?v=eaf4j19_3Zg

• Promonitor Test on Protein Synthesis, Mutations, Lac Operon, Homeobox Genes and Apoptosis tomorrow (Thursday).

• Today we shall complete Meiosis.

And so to Meiosis. Starter from Ryan,

Chelsea, Becky and Kelly.

• Meiosis is reduction division - ……………• Meiosis produces __________.• http://www.cellsalive.com/meiosis.htm

• Now work through the Meiosis booklet and animations. Each person will need a plasticine chromosome, replicated into chromatids and with the same 2 coloured beads on one end, but of a different colour to their partner’s.

• http://www.youtube.com/watch?v=kVMb4Js99tA&NR=1&feature=endscreen

• http://www.youtube.com/watch?v=eaf4j19_3Zg Meiosis square dance• http://highered.mcgraw-hill.com/sites/0072437316/student_view0/chapter12/

animations.html#

Meiosis cut and stick

• Check up to page 8, then pages 9 and 10.

• See next few slides about mutations in meiosis.

• http://www.youtube.com/watch?v=eaf4j19_3Zg Meiosis square dance

• http://highered.mcgraw-hill.com/sites/0072437316/student_view0/chapter12/animations.html#

Chromosome Mutations

• Can you see what happens when a deletion, inversion, and translocation occur?

Non-disjunction at metaphase 1

Now complete page 10, then check pages 11 – 14.Research physical effects of abnormalities in number of sex chromosomes if there is time.

AIMShttp://www.youtube.com/watch?v=eaf4j19_3Zg Meiosis square dance

• Collect in questions/tasks page 11 – 14 in Meiosis booklet for me to mark.

• Recap sources of variation – can you name four? http://highered.mcgraw-hill.com/sites/0072437316/student_view0/chapter12/animations.html#

• Give back promoniter test 5• Chromosome mutations – briefly.• Check Genetics homework - Use text books page

122 onwards and slides 24 – 26 on emailed pp to complete pages 1 – 5 of “Genetics” booklet.

• Codominance.• Dihybrid Crosses.

Homework – Question 5, 6, 7 , 8a) and b)Also, more co-dominance, more dihybridquestions and stretch and challenge p 127.

GENETICS AT A2

TOPICS TO BE COVERED

• Genetics Terminology• Monohybrid Crosses (as done at school)• Codominance• Dihybrid Crosses• Inheritance of Sex-linked Alleles• Epistasis• Testing the Significance of the

Outcomes of Breeding Programmes by the Chi ² Test

• Continuous and discontinuous variation

Terminology

• GENE – a length of ____ that codes for the production of a ___________ molecule.

• GENETIC CODE – • ALLELES – different forms of one

gene, e.g………………• LOCUS – the position of a gene on

a _______________ and on its homologous partner.

• GENOTYPE – the 2 alleles which an organism possesses for a particular gene, e.g. CC, Cc or cc.

• PHENOTYPE – the expression of the genotype e.g. a person either has cystic fibrosis or not.

• DOMINANT – only one of this allele needs to be present for the allele to be ______________ in the p_________.

• RECESSIVE – two of these alleles need to be present for…………..

CODOMINANCE – both alleles are equally dominant and so both expressed in the _____________.

So both C R (red pigment) and C W (white pigment) are expressed if together in a genotype.

The phenotype will therefore be………..

And finally…….

• LINKAGE - 2 or more genes are located (linked) on the same chromosome.

Tall plant

Smooth seed

Linkage reduces the possible combinations of genes during meiosis and therefore reduces thephenotypes resulting from a cross.

So, no ____________ ______________ at ___________ __

Gregor Mendel

Pea Breeding Programmes

An example of?

AIMS http://www.youtube.com/watch?v=we9_CdNPuJg&feature=related

• Monohybrid starter• Check homework questions page 4• Codominance• Dihybrid Inheritance• Sex – linkage if time • Homework – page 5 of booklet,

question 4, 5, 6 and 7 on sheet + active revision for test on Wednesday.

Monohybrid crosses

• Monohybrid crosses only take account of one feature, controlled by one gene at one locus on a chromosome.

• Genetic diagrams (Punnett squares) are used to show predicted genotypes of offspring.

• Use the accepted system for showing dominant and recessive alleles.

• Work through the examples on the next slide and then continue on page 4 and 5.

Easy!

Remember…• Monohybrid crosses – 2 alleles

(letters) in the genotypes but only 1 in the gametes.

R R

r

r

Always ask first:

What are the genotypes of the parents?

Monohybrid cross examples - starter

• Cystic fibrosis is caused by a faulty protein produced by a recessive allele c.

• The normal allele for the protein is C (dominant).1. Draw diagrams to show the offspring probabilities when: a) a woman with the condition has children with a healthy

homozygous man. All children are Cc so are carriers.b) Heterozygote parents have children. 1:2:1, CC, Cc, cc, so 1 in 4 chance of cf.2. A woman with genotype CC has children: 50% are ‘carriers’ Cc What is the genotype of the father? Cc – now check pages 4 and 5 in booklet.

Genetics continued• http://www.youtube.com/watch?v=f_3Utmj4RPU

• http://www.youtube.com/watch?v=we9_CdNPuJg&feature=related

• Codominance page 6 and 7

Fainting goats!

What are their codominant genotypes?

See question 1, page 6