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ARCH2108 Animals, plants and people. Week 2 Animal genetics Taxonomy and nomenclature. The eukaryote cell. The nucleus contains chromosomes. Chromosomes can be arranged to form a Karyotype. Human male karyotype. Total number of chromosomes is called diploid But chromosomes are paired

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ARCH2108 Animals, plants and people

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ARCH2108Animals, plants and people

Week 2

Animal genetics

Taxonomy and nomenclature


The eukaryote cell


The nucleus contains chromosomes.Chromosomes can be arranged to form a Karyotype

Human male karyotype


  • Total number of chromosomes is calleddiploid

  • But chromosomes are paired

  • The unpaired chromosome complement is called haploid

  • The diploid chromosome number is referred to as 2n

  • The human diploid number is given as

  • 2n = 46


Different species often have different karyotypesFour species of sheep

Domestic sheep

Ovis aries

Esfahan mouflon

Ovisorientalis

2n = 54

2n = 54

2n = 58

2n = 56

Tadjik urial

Ovis vignei

Argali

Ovis ammon


Banded

human karyotype


Some loci along human chromosome 7


What happens during formation of ova and sperm - 1

One diploid cell

Two diploid

cells


What happens during formation of ova and sperm - 2

Two diploid

cells

Four haploid cells


A pair of homologous chromosomes

Dominant alleles

Recessive alleles

An eye-colour locus

Blue-eyed allele

Brown-eyed allele

A blood-group locus

A allele

O allele


Homologous mutations

  • Because of the structure of DNA, the same mutations (mistakes in replication) recur independently in different individuals and in different species. (Homologous mutations).

  • These mutations are generally recessive.

  • Loci dealing with the same phenotypic character are often also arranged in an order of dominance.


Agouti (banded) hair

Agouti

Eumelanin

Phaeomelanin

Non-agouti


The Agouti locus:

Agouti Abyssinian

Aw

B

C

D

S

Ta

+Y


Interaction between the Agouti and Brown loci:Black agouti

A

B

D

C

Ss

T(+)

+Y


The Brown locus:Non-agouti black

aa

B

C

D

ss

T?

o (o or Y)


The Brown locus:

Nonagouti brown

aa

bb

C

D

ss

T?

O (o or Y)


The Chinchilla locus:Burmesesomewhat temperature-sensitive

aa

B

cb cb

D

ss

T?

O (o or Y)


The Chinchilla locus: Siamesetemperature-sensitive

aa

B

cscs

D

ss

T?

o (o or Y)


The Dilute locusDilute tabby (left) and dilute calico (right)

aa

B

C

d

Ss

T?

Oo

A

B

C

d

ss

T(T or tb)

o (or or Y)


The White Spotting locus

aa

B

C

D

Ss

T?

Oo

Homozygous

Heterozygous

aa

B

C

D

SS

T?

oo and oY


The Tabby locus

Mackerel

T(+)

Abyssinian

Ta

Blotched

Tb


The Orange sex-linked locus

Heterozygote (female only)

Calico or Tortoiseshell

Homozygote

Ginger

aa

B

C

D

Ss

T

Oo

?

?

C

D

ss

Tbtb

OY


The Mary Lyon effect(dosage compensation)

  • Females have two X chromosomes, males only one

  • One X is inactivated in each cell, so the sexes make equivalent amounts of X-chromosome gene product

  • Random X inactivation occurs in each cell early in foetal development

  • So the same active X chromosome is present in whole cell lines

  • Hence the patchwork effect in calico cats.


Other mutations(at different loci)

Silver (loss of phaeomelanin)

White

Manx

Cornish Rex

(curly coated)


Homologous mutations in other felids

White tiger

cch

Black leopard

B (but recessive)


Taxonomy

  • Species –

    • A population (or series of populations) diagnosably* distinct from all others.

      • *with fixed heritable differences

      • *absolutely different

    • Often (not invariably) reproductively distinct.

      • Preferring not to breed with other species

      • Not, as a rule, subject to gene-flow from other species

        NOTE WELL: THERE IS NO REQUIREMENT THAT INTERSPECIFIC HYBRIDS ARE STERILE


Domestic species

  • Products of artificial (human) selection

  • Distinction from wild species may be arbitrary, artificial

  • Often more variable than wild species, both individually and between artificially-maintained breeds

  • Nevertheless it is convenient to regard them (or those that differ diagnosably from their wild representatives) as species distinct from wild forms


Binomial nomenclature

  • Each species’ name has two words:

    • Generic name

      • Always begins with a capital letter

    • Specific name

      • Always begins with a small letter

Write them both in italics

Example:Canis lupus – the Gray Wolf

There are other species of the genus Canis, such as –

Canis rufus – the Red Wolf

Canis latrans – the Coyote

Canis aureus – the Golden Jackal

Canis mesomelas – the Black-backed Jackal


- And the domestic dog

  • Derived from Canis lupus, but we adopt the convenient fiction that it is a different species

    • Canis familiaris

The manybreeds of dog are at least as different from each other as they are from the gray wolf, but we do not refer to them by different specific names.

Feral dogs are sometimes given their own binomials, but there is no convention on this:

Canis dingo – the Dingo

Canis hallstromi – the New Guinea Singing Dog

Canis tenggeranus– the Tengger Dog


A genus

  • Is a monophyletic* group of species

    • *derived from an common ancestor exclusive to them

  • with a particular time depth

    • Usually taken to be ± 6 million years


A family

  • Is a monophyletic group of genera

  • with a particular time depth

    • Usually taken to be ± 24 million years

    • Name ends in –idae

    • Name is not written in italics

  • Divisions within families are called subfamilies

  • Name ends in –inae

  • Divisions within subfamilies are called tribes

  • Name ends in -ini


An order

  • Is a monophyletic group of families

  • With a particular time-depth

    • - Usually taken to be ± 65 million years

    • - No standard ending

    • - Not written in italics

  • A class

  • A phylum

  • A kingdom


The Orders ofEutherianMammals

*order has domestic representatives

*

*

*

*

*


Perissodactyla and Artiodactylaboth are ungulates (hoofed)but feet are different

Artiodactyla

Perissodactyla


Carnivora

Generally a

Sagittal crest

Carnassials

(P4 and M1)

Large canines


Rodentia and Lagomorpha

Lagomorpha have a diminutive

I2

Chisel-like incisors


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